n.
 the short, thick first digit of the hand, set lower and apart from the other four and opposable to them.
v.
   - press, touch, or indicate with one's thumb.
 - turn over (pages) with or as if with one's thumb. 
▸
[usu. as adj. thumbed]
 wear or soil (a book's pages) by repeated handling.
 - request or obtain (a free ride in a passing vehicle) by signalling with one's thumb.
 
 
  Phrase
  
    - thumb one's nose at
 informal show disdain or contempt for. 
[with ref. to the gesture of putting one's thumb on one's nose and spreading the fingers.]
  - thumbs up 
(or down)
 informal an indication of satisfaction or approval (or of rejection or failure). 
[with ref. to the signal of approval or disapproval used by spectators at a Roman amphitheatre (although the Romans used the symbols in reverse).]
  - under someone's thumb
 completely under someone's influence or control. 
   
  Derivative
  
    - thumbed adj.
  - thumbless adj.
 
   
  Etymology
  OE thūma, of W. Gmc origin.