Source : Webster's Revised Unabridged Dictionary (1913)

Quadrennial \Quad*ren"ni*al\, a. [L. quadriennium a space of
   four years; quattuor four + annus year; cf. L. quadriennis.
   See {Quadrate}, and {Annual}.]
   1. Comprising four years; as, a quadrennial period.

   2. Occurring once in four years, or at the end of every four
      years; as, quadrennial games.