Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

September, bris, m. [septem; as, October, Novem-ber, Decem-ber; cf. Varr. L. L. 6, § 34 Müll.], the seventh month of the Roman year, reckoning from March, i. e. our ninth, September (consisting, as now, of thirty days); usually with mensis: mense Septembri, Cic. Att. 1, 1, 2; Suet. Aug. 31; 35; id. Tib. 26; id. Calig. 15; id. Dom. 13 fin.
Without mensis, Aus. Ecl. de Mens. Monos. 9; so id. ib. Dist. 18; id. ib. Quot. Kal. 8 al.
As adj., with other substantives, of September, September-: Kalendis Septembribus, Cic. Fam. 14, 22; XIX. Kal. Septemb. (Aug. 14); XIII. Kal. Septemb. (Aug. 20), etc. … pridie Kal. Septemb. (Aug. 31)Calendis Septemb. … quarto Nonas Septemb. (Sept. 2) … Non. Septemb. (Sept. 5) … VII. Idus Septemb. (Sept. 7) … tertio Idus Septembris (Sept. 11) … Id. Sept. (Sept. 13), Col. 11, 2, 57 sq.: Idibus Septembribus, Liv. 7, 3; so Suet. Caes. 83: Septembribus horis, in the (unhealthy) time of September, Hor. Ep. 1, 16, 16 Schneid.