thumb

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The short thick digit of the human hand, next to the index finger and opposable to each of the other four digits.
2. n. A corresponding digit in other animals, especially primates. Also called pollex.
3. n. The part of a glove or mitten that covers the thumb.
4. n. Architecture An ovolo.
5. v. To scan (written matter) by turning over pages with or as if with the thumb.
6. v. To disarrange, soil, or wear by careless or frequent handling.
7. v. Informal To solicit (a ride) from a passing vehicle by signaling with the thumb.
8. v. To scan written matter by turning over pages with or as if with the thumb: thumbed through the latest issue of the magazine.
9. v. Informal To hitchhike.
10. idiom. all thumbs Lacking physical coordination, skill, or grace; clumsy.
11. idiom. thumb (one's) nose To express scorn or ridicule by or as if by placing the thumb on the nose and wiggling the fingers.
12. idiom. thumbs down An expression of rejection, refusal, or disapproval.
13. idiom. thumbs up An expression of approval, success, or hope.
14. idiom. under (one's) thumb Under the control of someone; subordinate to.

Century Dictionary and Cyclopedia

1. n. In geology, a columnar projection of eruptive rock.
2. To cover with the thumb, as the vent of a muzzle-loading cannon.
3. n. The shortest and thickest finger of the human hand; the pollex; the first digit of the hand, on the radial side, next to the index or forefinger. The perfected thumb is the chief characteristic of the human hand as distinguished from that of all other animals. This perfection is seen in the free movements of the member, and its ready apposability to any one of the other digits or to them all together. The extent to which it stands away from the rest indicates the great power and accuracy with which the hand may be used in grasping, as a prehensile organ, as in holding a pen or a knife. Such freedom and versatility are accomplished by the peculiar construction of the joint at the base of that metacarpal which supports the thumb. This articulation with the carpal bone called the trapezium is by means of reciprocally saddle-shaped articular surfaces, having the ease and extent of movement of a ball-and-socket or universal joint, though by a different mechanism. It is the only instance of such an articulation in the human body. The metacarpal bone of the thumb also differs from the rest in its mode of ossification, having, like the phalanges, a proximal and not a distal epiphysis—that is, the gristly cap that ossifies separately from the rest of the bone is on the end of the bone next to the wrist. The thumb is also peculiar in having but two joints or phalanges, the other digits having three apiece. The thumb is likewise moved by more muscles than those which actuate any other digit. They are a long deep flexor, and three separate long extensors (one for each phalanx and for the metacarpal bone), these four muscles coming to the thumb from high up in the forearm; and also several short muscles confined to the hand, the short flexor, the abductor, the adductor, and the opponens—altogether eight muscles in long and short sets of four each. The short muscles form the thenar eminence, or fleshy ball of the thumb.
4. n. The inner, radial, or first digit of the fore paw of any animal. When there are five digits, the first of these always corresponds to the human thumb; otherwise not.
5. n. The movable radial digit of a bird's manus or pinion, which bears the packet of feathers called the alula or bastard wing, and which is usually movable apart from the rest of the bones. By some it is supposed to correspond to the human thumb. It is more probably the homologue of the index or forefinger. See cut under pinion.
6. n. The thumb of the foot; the hallux; the inner digit of the foot, called the great toe in man. In quadrumanous or four-handed animals, as monkeys, opossums, and some others, it functions as a thumb, stands apart from the other digits, and so converts the hind foot into a grasping member, or “hand.” Its condition in man is quite exceptional in comparison with those animals to which he is nearest allied zoölogically.
7. n. The hind toe of a bird (except a three-toed woodpecker); the hallux; when there are two hind toes, the inner one of these (except in trogons). It is functionally a thumb, opposing other digits, and fitting the foot for grasping or perching. It is often absent or very small and functionless. Its length, low insertion, and entire freedom of movement are highly characteristic of the passerine series of birds, and varying conditions of its principal flexor tendon give rise to nomopelmous and correlated terms.
8. To handle or perform awkwardly: as, to thumb over a tune.
9. To soil or wear out with much handling; hence, to use, read, or turn over the pages of (as a book).
10. To turn (one's glass) over the thumb: an old custom when persons were drinking together, intending to show that the glass had been emptied so that the small drop remaining would lie on the thumb-nail without running off. Compare supernaculum.
11. n. Palpitation of the heart in domestic animals, as the horse, the result of functional or organic disease. See palpitation.

Wiktionary

1. n. The short thick digit of the hand that for humans has the most mobility and can be made to oppose (moved to touch) all of the other fingers.
2. n. The part of a slider that may be moved linearly along the slider.
3. n. thumbnail (picture).
4. v. To touch with the thumb.
5. v. To turn the pages of (a book) in order to read it cursorily.
6. v. To hitchhike

GNU Webster's 1913

1. n. The short, thick first digit of the human hand, differing from the other fingers in having but two phalanges; the pollex. See pollex.
2. v. To handle awkwardly.
3. v. To play with the thumbs, or with the thumbs and fingers.
4. v. To soil or wear with the thumb or the fingers; to soil, or wear out, by frequent handling; also, to cover with the thumb.
5. v. To play with the thumb or thumbs; to play clumsily; to thrum.

WordNet 3.0

1. v. feel or handle with the fingers
2. n. the part of a glove that provides a covering for the thumb
3. n. a convex molding having a cross section in the form of a quarter of a circle or of an ellipse
4. v. travel by getting free rides from motorists
5. n. the thick short innermost digit of the forelimb
6. v. look through a book or other written material