Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
strēnŭĭtas, ātis, f. [strenuus], nimbleness, briskness, vivacity, activity (very rare; perh. only in the two foll. passages): ab strenuitate et nobilitate strenui et nobiles, Varr. L. L. 8, § 15 Müll.: strenuitas antiqua manet, Ov. M. 9, 320.