Where does “quinquennio” come from?
quinquennio (Italian) comes from Latin quīnquennium, from Latin quinquennis, from Latin annus, from Proto-Italic atnos, from Proto-Indo-European h₂et-no-, from Proto-Indo-European h₂et- — grass.
quinquennio (Italian): five years, quinquennium
Ancestry of “quinquennio”, step by step