noun The short, thick first digit of the human hand, set lower and apart from the other four and opposable to them.
verb Press, move, or touch (something) with one's thumb. (as soon as she thumbed the button, the door slid open) Turn over (pages) with or as if with one's thumb. (I've thumbed my address book and found quite a range of smaller hotels) Request or obtain (a free ride in a passing vehicle) by signalling with one's thumb. (three cars passed me and I tried to thumb a lift)