Tit
mid 16th century: probably of Scandinavian origin and related to Icelandic titlingur ‘sparrow’; compare with titling2 and titmouse. Earlier senses were ‘small horse’ and ‘girl’; the current sense dates from the early 18th century.
wiktionary
From Middle English tit, titte, tette, from Old English tit, titt, from Proto-Germanic *titt-(“teat; nipple; breast”), of expressive origin.
Perhaps related to an original meaning “to suck”; compare Proto-Indo-European *dʰeh₁-y-. Doublet of teat, which was borrowed from Old French.
Perhaps imitative of light tap. Compare earlier tip for tap(“blow for blow”), from tip + tap; compare also dialectal tint for tant.
Probably of North Germanic/Scandinavian origin; found earliest in titling and titmouse; compare Faroese títlingur, dialectal Norwegian titling(“small stockfish”), which could ultimately be from a base alluding to diminutive size; compare the first element of titbit. [1]
etymonline
tit (n.1)
"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.).
tit (n.2)
1540s, a word used for any small animal or object (as in compound forms such as titmouse, tomtit, etc.); also used of small horses. Similar words in related senses are found in Scandinavian (Icelandic tittr, Norwegian tita "a little bird"), but the connection and origin are obscure; perhaps, as OED suggests, the word is merely suggestive of something small. Used figuratively of persons after 1734, but earlier for "a girl or young woman" (1590s), often in deprecatory sense of "a hussy, minx."
