Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sĭmĭlĭtas, ātis, f. [similis] a rare form for similitudo, likeness, resemblance, similarity: morum, Caecil. ap. Non. 177, 2 (Com. Rel. v. 216 Rib.).
Plur.: naturae rerum similitates, Vitr. 2, 9 med.