quartānus, a, um, adj. id., of or belonging to the fourth; esp., Of or occurring on the fourth day, quartan: febris, Cic. N. D. 3, 10, 24; Plin. 7, 50, 51, § 166; Mart. 10, 77, 3.

— Hence, as subst.: quar-tāna, ae, f. (sc. febris), an ague occurring every fourth day, a quartan ague (class.): in quartanam conversa vis est morbi, Cic. Fam. 16, 11, 1; cf. Cels. 2, 1, 20; Plin. 22, 25, 72, § 150: frigida, Hor. S. 2, 3, 290.

— Of or belonging to the fourth legion; plur. as subst.: quartāni, m., the soldiers of the fourth legion, Tac. H. 4, 37; Inscr. Orell. 3118.