(anatomy, informal) The fleshy portion, opposite the nail, of the first segment (first phalange) of the human thumb.

(games) A children's game in which the two opponents interlock each other's right- or left-handed fingers, each attempting to press and subdue the other's thumb.

(US, intransitive, idiomatic) To hitchhike.

A fairy-tale character who is the size of a person's thumb; the protagonist and hero of the fairy tale The History of Tom Thumb.

An overhand knot.

The European bullhead (“a species of fish, Cottus gobio”).

plural of miller's thumb

(computing) A small electronic device used to store digital data, more portable and robust than a hard drive.

A crude representation, as if drawn with the thumb

Alternative spelling of thumb-sketch