Inherited from Old French tete, probably from Frankish or West Germanic *titta, from Proto-Germanic *titt- (“teat; nipple; breast”), from Proto-Indo-European *tata- (“father; parent; nipple”).
Compare Dutch tiet, German Zitze, English tit, teat. Compare also Late Latin titta, Italian tetta, Spanish teta. Possibly ultimately an expressive formation found in many languages.