Where does “κατεπάνω” come from?

κατεπάνω (Ancient Greek) comes from Ancient Greek ἐπάνω, from Ancient Greek ἐπί, from Ancient Greek Ἡμέρα, from Ancient Greek ἦμαρ, from Proto-Hellenic ā́mər, from Proto-Indo-European h₂eh₃mr̥, from Proto-Indo-European h₂eh₃- — to be hot; to burn.

κατεπάνω (Ancient Greek): title of Byzantine governors