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focus - 12 dictionary results
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fo⋅cus

  [foh-kuhs] noun, plural -cus⋅es, -ci  [-sahy, -kahy] , verb, -cused, -cus⋅ing or (especially British) -cussed, -cus⋅sing.
Use focus in a Sentence
–noun
1. a central point, as of attraction, attention, or activity: The need to prevent a nuclear war became the focus of all diplomatic efforts.
2. Physics. a point at which rays of light, heat, or other radiation, meet after being refracted or reflected.
3. Optics.
a. the focal point of a lens.
b. the focal length of a lens.
c. the clear and sharply defined condition of an image.
d. the position of a viewed object or the adjustment of an optical device necessary to produce a clear image: in focus; out of focus.
4. Geometry. (of a conic section) a point having the property that the distances from any point on a curve to it and to a fixed line have a constant ratio for all points on the curve.
5. Geology. the point of origin of an earthquake.
6. Pathology. the primary center from which a disease develops or in which it localizes.
–verb (used with object)
7. to bring to a focus or into focus: to focus the lens of a camera.
8. to concentrate: to focus one's thoughts.
–verb (used without object)
9. to become focused.
Origin:
1635–45; < L: fireplace, hearth

Related forms:
fo⋅cus⋅a⋅ble, adjective
fo⋅cus⋅er, noun

Synonyms:
1. center, heart, core, nucleus.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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focal length  
n.   Abbr. f
The distance from the surface of a lens or mirror to its focal point. Also called focal distance, focus.
fo·cus   (fō'kəs)   
n.   pl. fo·cus·es or fo·ci (-sī', -kī')
    1. A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system: the focus of a lens. Also called focal point.
    2. See focal length.
    3. The distinctness or clarity of an image rendered by an optical system.
    4. The state of maximum distinctness or clarity of such an image: in focus; out of focus.
    5. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear: a camera with automatic focus.
    1. The distinctness or clarity of an image rendered by an optical system.
    2. The state of maximum distinctness or clarity of such an image: in focus; out of focus.
    3. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear: a camera with automatic focus.
  3. A center of interest or activity. See Synonyms at center.
  4. Close or narrow attention; concentration: "He was forever taken aback by [New York's] pervasive atmosphere of purposefulness—the tight focus of its drivers, the brisk intensity of its pedestrians" (Anne Tyler).
  5. A condition in which something can be clearly apprehended or perceived: couldn't get the problem into focus.
  6. Pathology The region of a localized bodily infection or disease.
  7. Geology The point of origin of an earthquake.
  8. Mathematics A fixed point whose relationship with a directrix determines a conic section.
v.   fo·cused or fo·cussed, fo·cus·ing or fo·cus·sing, fo·cus·es or fo·cus·ses

v.   tr.
  1. To cause (light rays, for example) to converge on or toward a central point; concentrate.
    1. To render (an object or image) in clear outline or sharp detail by adjustment of one's vision or an optical device; bring into focus.
    2. To adjust (a lens, for example) to produce a clear image.
  3. To direct toward a particular point or purpose: focused all their attention on finding a solution to the problem.
v.   intr.
  1. To converge on or toward a central point of focus; be focused.
  2. To adjust one's vision or an optical device so as to render a clear, distinct image.
  3. To concentrate attention or energy: a campaign that focused on economic issues.

[Latin, hearth.]
fo'cus·er n.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Focus

Fo"cus\, n.; pl. E. Focuses, L. Foci. [L. focus hearth, fireplace; perh. akin to E. bake. Cf. Curfew, Fuel, Fusil the firearm.]

1. (Opt.) A point in which the rays of light meet, after being reflected or refrcted, and at which the image is formed; as, the focus of a lens or mirror.

2. (Geom.) A point so related to a conic section and certain straight line called the directrix that the ratio of the distace between any point of the curve and the focus to the distance of the same point from the directrix is constant.

Note: Thus, in the ellipse FGHKLM, A is the focus and CD the directrix, when the ratios FA:FE, GA:GD, MA:MC, etc., are all equal. So in the hyperbola, A is the focus and CD the directrix when the ratio HA:HK is constant for all points of the curve; and in the parabola, A is the focus and CD the directrix when the ratio BA:BC is constant. In the ellipse this ratio is less than unity, in the parabola equal to unity, and in the hyperbola greater than unity. The ellipse and hyperbola have each two foci, and two corresponding directrixes, and the parabola has one focus and one directrix. In the ellipse the sum of the two lines from any point of the curve to the two foci is constant; that is: AG+GB=AH+HB; and in the hyperbola the difference of the corresponding lines is constant. The diameter which passes through the foci of the ellipse is the major axis. The diameter which being produced passes through the foci of the hyperbola is the transverse axis. The middle point of the major or the transverse axis is the center of the curve. Certain other curves, as the lemniscate and the Cartesian ovals, have points called foci, possessing properties similar to those of the foci of conic sections. In an ellipse, rays of light coming from one focus, and reflected from the curve, proceed in lines directed toward the other; in an hyperbola, in lines directed from the other; in a parabola, rays from the focus, after reflection at the curve, proceed in lines parallel to the axis. Thus rays from A in the ellipse are reflected to B; rays from A in the hyperbola are reflected toward L and M away from B.

3. A central point; a point of concentration.

Aplanatic focus. (Opt.) See under Aplanatic.

Conjugate focus (Opt.), the focus for rays which have a sensible divergence, as from a near object; -- so called because the positions of the object and its image are interchangeable.

Focus tube (Phys.), a vacuum tube for R[oe]ntgen rays in which the cathode rays are focused upon the anticathode, for intensifying the effect.

Principal, or Solar, focus (Opt.), the focus for parallel rays.

Focus

Fo"cus\, v. t. [imp. & p. p. Focused; p. pr. & vb. n. Focusing.] To bring to a focus; to focalize; as, to focus a camera. --R. Hunt.
Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
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Language Translation for : focus
Spanish: foco,
German: der Brennpunkt,
Japanese: 焦点
More Translations »

focus 
1644, from L. focus "hearth, fireplace," of unknown origin, used in post-classical times for "fire" itself, taken by Kepler (1604) in a mathematical sense for "point of convergence," perhaps on analogy of the burning point of a lens (the purely optical sense of the word may have existed before 1604, but it is not recorded). Introduced into Eng. 1656 by Hobbes. Sense transfer to "center of activity or energy" is first recorded 1796. The verb is first attested 1814 in the literal sense; the fig. sense is recorded earlier (1807).
Online Etymology Dictionary, © 2001 Douglas Harper
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Main Entry: 1fo·cus
Pronunciation: 'fO-k&s
Function: noun
Inflected Form: plural fo·ci /'fO-"sI also-"kI/ also fo·cus·es
1 a : a point at which rays (as of light, heat, or sound) converge or from which they diverge or appear to diverge;specifically : the point where the geometrical lines or their prolongations conforming to the rays diverging from or converging toward another point intersect and give rise to an imageafter reflection by a mirror or refraction by a lens or optical system b : a point of convergence of a beam of particles (as electrons)
2 a : FOCAL LENGTH b : adjustment for distinct vision; also : the area that may be seen distinctlyor resolved into a clear image
3 : a localized area of disease or the chief site of a generalized disease or infection

Main Entry: 2focus
Function: verb
Inflected Forms: fo·cused also fo·cussed; fo·cus·ing also fo·cus·sing
transitive senses
1 : to bring (as light rays) to a focus
2 a : to adjust the focus of (as the eye or a lens) b : to bring (as an image) into focus focus intransitive senses
1 : to come to a focus
2 : to adjust one's eye or a camera to aparticular range —fo·cus·able /-k&s-&-b&l/ adjective
Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
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focus fo·cus (fō'kəs)
n. pl. fo·cus·es or fo·ci (-sī', -kī')

  1. A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system. Also called focal point.
  2. See focal length.
  3. The distinctness or clarity of an image rendered by an optical system.
  4. The state of maximum distinctness or clarity of such an image.
  5. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear.
  6. The region of a localized bodily infection or disease.
v. fo·cused or fo·cussed, fo·cus·ing or fo·cus·sing, fo·cus·es or fo·cus·ses
  1. To cause light rays or other radiation to converge on or toward a central point; concentrate.
  2. To render an object or image in clear outline or sharp detail by adjustment of one's vision or an optical device.
  3. To adjust a lens or instrument to produce a clear image.
  4. To converge on or toward a central point of focus; be focused.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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focus   (fō'kəs)  Pronunciation Key 
Plural focuses or foci (fō'sī', fō'kī')
  1. The degree of clarity with which an eye or optical instrument produces an image.
  2. See focal point.
  3. A central point or region, such as the point at which an earthquake starts.
  4. Mathematics A fixed point or one of a pair of fixed points used in generating a curve such as an ellipse, parabola, or hyperbola.
  5. The region of a localized bodily infection or disease.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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FOCUS database, language
A hierarchical database language from Information Builders, Inc.
(1994-12-21)

The Free On-line Dictionary of Computing, © 1993-2007 Denis Howe
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FOCUS
Fisheries Oceanography Cooperative Users System
The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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