Sentence:  The original meaning of "πρύτανις" was 'chief magistrate' which metonymically could also be used of the ‘ruler, lord' (e.g. Zeus). It is no doubt rightly connected with the Etruscan magistrate's name "purθne, eprθni". Because of this, and because Aeolic has "πρότανις", Phocian and Cretan  "βρυτ-", it cannot be a native word but must be a borrowing. Hittite "hupurtanuri-" is an official's title, known from Ugarit. Laroche has interpreted it and the words "tuppalanuri-, tuppanuri-" as containing the adjective "uri-" ‘great', so that "tuppalan-uri" = ‘grand des scribes', "tuppan-uri" = ‘grand des tablettes'; this would leave us with a basic "huburtan-" which seems to have been taken over as "οπορταν-/οπροταν-" or "οπυρταν-/οπρυταν-", and by <WSD>deglutination</WSD> of the ‘article' gave "πρότανις/πρύτανις". 
Meaning of the word marked with <WSD> tags:  A process by which a formerly significant part of a combined term is clipped.