Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
perversĭtas, ātis, f. [perversus], frowardness, untowardness, perversity: quae est autem in hominibus tanta perversitas, ut, etc., Cic. Or. 9, 31: opinionum, id. Tusc. 3, 1, 2: magna perversitas, id. Off. 1, 40, 145: alicujus, id. Q. Fr. 1, 1, 13, § 38: molestissima diligentiae perversitas, Quint. 1, 6, 34: morum, Suet. Aug. 62: incredibilis hominum, Cic. Fam. 1, 7, 7.