Possible Definitions:
1. Thumb (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. Thumb (v. t.) To handle awkwardly.
3. Thumb (v. t.) To play with the thumbs, or with the thumbs and fingers; as, to thumb over a tune.
4. Thumb (v. t.) To soil or wear with the thumb or the fingers; to soil, or wear out, by frequent handling; also, to cover with the thumb; as, to thumb the touch-hole of a cannon.
5. Thumb (v. i.) To play with the thumb or thumbs; to play clumsily; to thrum.
