n. & v.
n. 1 a a short thick terminal projection on the human hand, set lower and apart from the other four and opposable to them. b a digit of other animals corresponding to this. 2 part of a glove etc. for a thumb.
v. 1 tr. wear or soil (pages etc.) with a thumb (a well-thumbed book). 2 intr. turn over pages with or as with a thumb (thumbed through the directory). 3 tr. request or obtain (a lift in a passing vehicle) by signalling with a raised thumb. 4 tr. use the thumb in a gesture. be all thumbs be clumsy with one's hands. thumb index n. a set of lettered grooves cut down the side of a diary, dictionary, etc. for easy reference.
v.tr. provide (a book etc.) with these. thumb one's nose = cock a snook (see SNOOK(1)). thumb-nut a nut shaped for turning with the thumb and forefinger. thumbs down an indication of rejection or failure. thumbs up an indication of satisfaction or approval. under a person's thumb completely dominated by a person. thumbed adj. (also in comb.). thumbless adj.
[ OE thuma f. a WG root = swell ]