Source : Webster's Revised Unabridged Dictionary (1913)

Quinquennial \Quin*quen"ni*al\, a. [L. quinquennalis and
   quinquennis; quinque five + annus year. See {Five}, and cf.
   {Biennial}.]
   Occurring once in five years, or at the end of every five
   years; also, lasting five years. A quinquennial event.