Etymology tree
Proto-Indo-European *h₁eḱ-
Proto-Indo-European *h₁éḱwos
Proto-Italic *ekwos
Latin equus
Inherited from Proto-Italic *ekwos, from Proto-Indo-European *h₁éḱwos (“horse”). Cognate with Ancient Greek ἵππος (híppos), Sanskrit अश्व (áśva), Persian اسب (asb), Old Armenian էշ (ēš, “donkey”), Tocharian B yakwe, and Gaulish epos.
Respelt with ⟨quu⟩ for the earlier ⟨quo⟩/⟨cu⟩ in post-Augustan times on the analogy of oblique cases.