Lewis Short
(adjective) : Sextīlis, e, sextus
* Sixth, only with mensis, of the month of August: MENSE SEXTILI, S. C. ap. Macr. S. 1, 12 fin.: Sextili menso caminus,Hor. Ep. 1, 11, 19. —Hence, subst.: Sextīlis, is, m. (sc. mensis), the sixth (month); hence, the month of August, acc. to the old Roman reckoning (counting from March), afterwards called Augustus (v. h. v., and cf. Varr. L. L. 6, 4 fin.), Cic. Fam. 10, 26, 1: Sextilem totum mendax desideror,Hor. Ep. 1, 7, 2: Kalendae,of August,Liv. 3, 6; 6, 1 fin.: Nonae, Idus,id. 41, 16.
Charlton T. Lewis, Charles Short, A Latin Dictionary