Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
quinquennis, e, adj. [quinqueannus], of five years or five years old: filia, Plaut. Poen. prol. 85: Olympias, celebrated every fifth year, quinquennial, Ov. P. 4, 6, 5: vinum, Hor. S. 2, 8, 47: oleae, id. ib. 2, 2, 57: juvenis, Col. 7, 3, 6.
Plur. as subst.: quinquennĭa, ōrum, n., for quinquennālĭa, ium, games celebrated every fifth year, Stat. S. 5, 3, 113.