teat (n.)

"breast," Old English titt "teat, nipple, breast" (a variant of teat). But the modern slang tits (plural), attested from 1928, seems to be a recent reinvention, used without awareness of the original form, from teat or from dialectal and nursery diminutive variant titties (pl.).

1530s, nyppell, "protuberance of a mammalian breast," in a female the extremity where the milk-ducts discharge, alteration of neble (1520s), probably diminutive of neb "bill, beak, snout" (see neb), hence, literally "a small projection." Used from 1713 of any thing or mechanical part that projects like a nipple. From 1875 in reference to the mouthpiece of an infant's nursing-bottle. Earlier words were pap (n.2), teat. A 16c.-17c. slang term for a woman's nipples was cherrilets.

1746, tetties (plural), a nursery or dialect diminutive variant of teats (see teat).

Margery. Come, be quite;—be quite, es zey, a grabbling o' wone's Tetties.—Es wont ha' ma Tetties a grabbled zo ; ner es wont be mullad and foulad.—Stand azide; come, gi' o'er. ["Exmoor Courtship, or, A Suitoring Discourse, in the Devonshire Dialect and Mode, near the forest of Exmoor," 1746]