tit

A teat.

Any of various small insectivorous songbirds of the family Paridae of woodland areas, especially those of Eurasia and Africa.

In the phrase tit for tat (literally, in the original form tip for tap, ‘blow for blow’), a retaliatory return; an equivalent by way of repartee or answer: as, to give a person tit for tat in a dispute or a war of wit.

In mech., a round projection on a tool or other piece to serve as a guide. A tit is usually made on the end of a counterbore, so that the hole made by it shall be concentric with the hole which it is desired to enlarge.