Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
quinquertĭum, ii, n. [quinque-ars], the five sorts of bodily exercises for youth (discus, cursus, saltus, lucta, jaculatio): quinquertium vocabant antiqui, quem Graeci πένταθλον . . . Livius quoque (Andron.) ipsos athletas sic nominat: quinquertiones praeco in medium vocat, Fest. p. 257 Müll.; cf. Paul. ex Fest. p. 256 ib.