a solid geometric figure generated by the revolution of a semicircle about its diameter; a round body whose surface is at all points equidistant from the center. Equation: x 2 + y 2 + z 2 = r 2 .
the surface of such a figure; a spherical surface.
any rounded body approximately of this form; a globular mass, shell, etc.
a planet or star; heavenly body.
any of the transparent, concentric, spherical shells, or layers, in which, according to ancient belief, the planets, stars, and other heavenly bodies were set.
the place or environment within which a person or thing exists; a field of activity or operation: to be out of one's professional sphere.
a particular social world, stratum of society, or walk of life: His social sphere is small.
a field of something specified: a sphere of knowledge.
verb (used with object), sphered, sphering.
to enclose in or as if in a sphere.
to form into a sphere.
to place among the heavenly spheres.

1250–1300; < Late Latin sphēra, Latin sphaera globe < Greek sphaîra ball; replacing Middle English spere < Old French spere < Late Latin spēra, variant of sphēra

sphereless, adjective
spherelike, adjective
subsphere, noun
unsphering, adjective

4. orbit, area, province, compass, realm, domain. 5. class, rank.
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
sphere (sfɪə)
1.  maths
 a.  a three-dimensional closed surface such that every point on the surface is equidistant from a given point, the centre
 b.  the solid figure bounded by this surface or the space enclosed by it. Equation: (x--a)² + (y--b)² + (z--c)² = r², where r is the radius and (a, b, c) are the coordinates of the centre; surface area: 4πr²; volume: 4πr³/3
2.  any object having approximately this shape; globe
3.  the night sky considered as a vaulted roof; firmament
4.  any heavenly object such as a planet, natural satellite, or star
5.  (in the Ptolemaic or Copernican systems of astronomy) one of a series of revolving hollow globes, arranged concentrically, on whose transparent surfaces the sun (or in the Copernican system the earth), the moon, the planets, and fixed stars were thought to be set, revolving around the earth (or in the Copernican system the sun)
6.  particular field of activity; environment: that's out of my sphere
7.  a social class or stratum of society
8.  to surround or encircle
9.  to place aloft or in the heavens
[C14: from Late Latin sphēra, from Latin sphaera globe, from Greek sphaira]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1530s, restored spelling of M.E. spere (c.1300) "space, conceived as a hollow globe about the world," from O.Fr. espere (13c.), from L. sphæra "globe, ball, celestial sphere," from Gk. sphaira "globe, ball," of unknown origin. Sense of "ball, body of globular form" is from late 14c. Medieval astronomical
meaning "one of the 8 (later 10) concentric, transparent, hollow globes believed to revolve around the earth and carry the heavenly bodies" is from late 14c.; the supposed harmonious sound they made rubbing against one another was the music of the spheres (late 14c.). Meaning "range of something" is first recorded c.1600 (e.g. sphere of influence (1885), in reference to British-German colonial rivalry in Africa). A spherical number (1640s) is one whose powers always terminate in the same digit as the number itself (5,6, and 10 are the only ones).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

sphere (sfēr)
A ball-shaped or a globular body.

spher'al (sfēr'əl) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
sphere   (sfîr)  Pronunciation Key 
A three-dimensional geometric surface having all of its points the same distance from a given point.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Their shells vary from simple tubes and spheres to elaborate, multi-chambered
  spirals and long, striated pods.
Insularism seems to be expected, or even encouraged in some spheres.
Religion makes visible the interplay between belief and behavior in various
  spheres of human activity.
The bolus of air breaks into three spheres that flatten into mushrooms the
  diameter of dinner plates, expanding as they climb.
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