Definition of: thumb

(thum) noun
1. The inner digit of a limb when set apart from and apposable to the other fingers; especially, the short, thick digit on the radial side of the human hand; the pollex.
2. Ornithol. The first radial digit of the wing of certain birds.
3. The division in a glove or mitten that covers the thumb.
4. Archit. An ovolo.
—all thumbs Colloq. Clumsy with the hands; not deft.
—thumbs down A sign of negation or disapproval.
—under one's thumb Under one's influence or power.
—v.t.
1. To press, rub, soil, or wear with the thumb in handling, as the pages of a book.
2. To perform with or as with the thumbs; hence, to do or handle clumsily.
3. To run through the pages of (a book, manuscript, etc.,) rapidly and perfunctorily.
4. To solicit or obtain (a ride) in an automobile by standing by the road and indicating with the thumb the direction one wishes to go; also, to make (one's way) thus: He thumbed his way to New York. [OE thūma]