Etymology tree Proto-Indo-European *ís? Proto-Indo-European *h₁óynos Proto-Italic *oinos Old Latin oinos Latin ūnus Proto-Indo-European *-yétider. Latin -iō Latin ūniō Proto-Indo-European *-tós Proto-Italic *-tos Latin -tus Latin ūnītuslbor. Middle English uniten English unite From Middle English uniten, from Latin ūnītus, perfect passive participle of ūniō.