noun: A period of four years.
From Latin quadri (four) + annus (year), ultimately from the Indo-European root at- (to go), which is also the source of annual, annals, annuity, anniversary, and perennial.
"Maybe it's because I'm an Olympic dad, but my wife and I had a baby each quadrennium."
Jean Lopez, et al.; Family Power; Celebra; 2009.