triennium

triennium ī, n

tres+annus; sc. spatium, three years' time, three years : triennium est, cum, etc.

triennium
trĭennĭum, ii, n. (sc. spatium) [tres-annus], the space of three years , three years : biennium aut...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.