Where does “शिरस्” come from?

शिरस् (Sanskrit) comes from Proto-Indo-Iranian ćŕ̥Has, from Proto-Indo-European ḱŕ̥h₂-os, from Proto-Indo-European ḱerh₂- — head, top; horn.

शिरस् (Sanskrit): head, skull; the upper end or highest part of...