the short, thick, inner digit of the human hand, next to the forefinger.
the corresponding digit in other animals; pollex.
the part of a glove or mitten for containing this digit.
Architecture. an ovolo or echinus molding.
verb (used with object)
to soil or wear with the thumbs in handling, as the pages of a book.
to glance through (the pages of a book, leaflet, etc.) quickly.
to play (a guitar or other instrument) with or as with the thumbs.
(of a hitchhiker) to solicit or get (a ride) by pointing the thumb in the desired direction of travel.
all thumbs, awkward; clumsy; bungling: The visitor almost knocked over a vase and seemed to be all thumbs.
thumb one's nose,
to put one's thumb to one's nose and extend the fingers as a crudely defiant or contemptuous gesture.
to express defiance or contempt; dismiss or reject contemptuously.
thumbs down, a gesture or expression of dissent or disapproval: We turned thumbs down to that suggestion.
thumbs up, a gesture or expression of assent or approval.
under one's thumb, under the power or influence of; subordinate to. Also, under the thumb of.

before 900; Middle English; Old English thūma; cognate with Dutch duim, Old Saxon, Old High German dūmo (German Daumen), Old Norse thumall; akin to Latin tumēre to swell (tumor)

thumbless, adjective
thumblike, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
thumb (θʌm)
1.  Technical name: pollex the first and usually shortest and thickest of the digits of the hand, composed of two short bonesRelated: pollical
2.  the corresponding digit in other vertebrates
3.  the part of a glove shaped to fit the thumb
4.  architect another name for ovolo
5.  all thumbs clumsy
6.  thumbs down an indication of refusal, disapproval, or negation: he gave the thumbs down on our proposal
7.  thumbs up an indication of encouragement, approval, or acceptance
8.  under someone's thumb at someone's mercy or command
vb (when intr, often foll by through)
9.  (tr) to touch, mark, or move with the thumb
10.  to attempt to obtain (a lift or ride) by signalling with the thumb
11.  to flip the pages of (a book, magazine, etc) perfunctorily in order to glance at the contents
12.  thumb one's nose at to deride or mock, esp by placing the thumb on the nose with fingers extended
Related: pollical
[Old English thūma; related to Old Saxon thūma, Old High German thūmo, Old Norse thumall thumb of a glove, Latin tumēre to swell]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

O.E. þuma, from W.Gmc. *thumon- (cf. O.Fris. thuma, O.S., O.H.G. thumo, Ger. Daumen, Du. duim "thumb," O.N. þumall "thumb of a glove"), lit. "the stout or thick (finger)," from PIE *tum- "swell" (cf. L. tumere "to swell," tumidus "swollen;" Avestan tuma "fat;" see
thigh). For spelling with -b (attested from c.1290), see limb. The verb meaning "to go through" (especially of printed material) is first found 1930, though the related sense of "soil or wear by handling" dates from 1644. Verb meaning "to hitchhike" is 1939, originally the thumb pointed in the direction one wished to travel. Thumbnail sketch (1852) so called for its smallness. To be under (someone's) thumb "be totally controlled by that person" is recorded from 1586. Thumbs up (1887) and thumbs down (1906) were said to be from expressions of approval or the opposite in ancient amphitheaters, especially gladiator shows, where the gesture decided whether a defeated combatant was spared or slain. But the Roman gesture was merely one of hiding the thumb in the hand or extending it. Perhaps the modern gesture is from the usual coachmen's way of greeting while the hands are occupied with the reins.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

thumb (thŭm)
The short thick digit of the human hand, next to the index finger and opposable to each of the other four digits.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Computing Dictionary

Thumb definition

An extension to the Advanced RISC Machine architecture, announced on 06 March 1995 by Advanced RISC Machines Ltd. By identifying the critical subset of the ARM instruction set and encoding it into 16 bits, ARM has succeeded in reducing typical program size by 30-40% from ARM's already excellent code density. Since this Thumb instruction set uses less memory for program storage, cost is further reduced.
All Thumb-aware processor cores combine the capability to execute both the 32-bit ARM and the 16-bit Thumb instruction sets. Careful design of the Thumb instructions allow them to be decompressed into full ARM instructions transparently during normal instruction decoding without any performance penalty. This differs from other 32-bit processors, like the Intel 486SX, with a 16-bit data bus, which require two 16-bit memory accesses to execute every 32-bit instruction and so halve performance.
The patented Thumb decompressor has been carefully designed with only a small amount of circuitry additional to the existing instruction decoder, so chip size and thus cost do not significantly increase. Designers can easily interleave fast ARM instructions (for performance critical parts of a program) with compact Thumb code to save memory.

thumb definition

The slider or "bubble" on a window system scrollbar. So called because moving it allows you to browse through the contents of a text window in a way analogous to thumbing through a book.
[Jargon File]
The Free On-line Dictionary of Computing, © Denis Howe 2010
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American Heritage
Idioms & Phrases


In addition to the idioms beginning with thumb, also see all thumbs; green thumb; rule of thumb; stick out (like a sore thumb); twiddle one's thumbs; under someone's thumb.

The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Encyclopedia Britannica


short, thick first digit of the human hand and of the lower-primate hand and foot. It differs from other digits in having only two phalanges (tubular bones of the fingers and toes). The thumb also differs in having much freedom of movement and being opposable to tips of other digits. The corresponding first digit (most medial digit) in other vertebrates is also called the thumb, especially if it has some manipulative or special ability (e.g., in the raccoon and the bat)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Press your thumb into center of each cookie ball, making a small well.
Don't use your thumb to direct water from a bare hose end.
She then pierced a hole in the center of the pancake with the back of her
  thumb, and laid it in the skillet.
They eat bamboo, grasping shoots with a pseudo thumb.
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