Where does “quinquennium” come from?
quinquennium (English) 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.
quinquennium (English): A period of five years
Ancestry of “quinquennium”, step by step