Extenuatio, ônis, f. g. Verbal. Ci. A diminishing or making lesse: an extenuating.
Lewis and Short: Latin dictionary
extĕnŭātĭo, ōnis, f. [extenuo], a thinning, rarefaction.I.Lit.: vitium, Plin. 17, 26, 39, 246; Sen. Q. N. 2, 57, 3.—II.Trop., a lessening, diminution, extenuation, as a figure of speech, the Gr. mei/wsis or e)la/ttwsis, Cic. de Or. 3, 53, 202; Quint. 9, 1, 28; 9, 2, 3.