Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prō-portĭo, ōnis, f., comparative relation, proportion, symmetry, analogy, likeness (class.): proportio, quod dicunt ἀνάλογον, Varr. L. L. 10, § 2 Müll.; Cic. Univ. 5: Penatis singulariter Labeo Antistius posse dici putat, quia pluraliter Penates dicantur: cum patiatur proportio etiam Penas dici, ut optimas, primas, Antias, Fest. s. v. penatis, p. 253 Müll.: id optime assequitur quae Graece ἀναλογία, Latine (audendum est enim, quoniam haec primum a nobis novantur) comparatio, proportiove dici potest, Cic. Univ. 4; Quint. 1, 6, 3 and 9: uti proportione, Varr. R. R. 1, 18, 3; Cic. Verr. 2, 4, 21, § 46.