Thumb  —n. 1 short thick finger on the human hand, set apart from the other four. 2 part of a glove etc. For a thumb. —v. 1 wear or soil (pages etc.) With a thumb. 2 turn over pages with or as with a thumb (thumbed through the directory). 3 request or get (a lift) by signalling with a raised thumb. 4 use the thumb in a gesture.  thumb one's nose = cock a snook (see *snook). Thumbs down indication of rejection. Thumbs up indication of satisfaction or approval. Under a person's thumb completely dominated by a person. [old english]