From Proto-Italic *fēlājō, from earlier Proto-Italic *θēlājō, from Proto-Indo-European *dʰeh₁(i)-l-éh₂-ye-ti, from Proto-Indo-European *dʰeh₁(y)- (“to suck, suckle”). Cognates include Sanskrit धयति (dhayati), Ancient Greek θηλή (thēlḗ), Gothic 𐌳𐌰𐌳𐌳𐌾𐌰𐌽 (daddjan, “suckle”), and Old Church Slavonic доити (doiti). Related to fēmina, fīlius, fētus.