Lewis & Short

sexus, ūs (abl. plur. sexibus, Spart. Hadr. 18, 10 al.; but sexubus, Jul. Val. Rer. G. Alex. 1, 36), m., or sĕcus, indecl. n. [root sec- of seco; hence properly, a division, segment].

  1. I. A sex, male or female (of men and beasts).
          1. (α) Form sexus: hominum genus et in sexu consideratur, virile an muliebre sit, Cic. Inv. 1, 24, 35; cf.: natus ambiguo inter marem ac feminam sexu infans, Liv. 27, 11; and: mare et femineum sexus, App de Mundo, c. 20, p. 66 med.: feminarum sexus, Plin. 7, 52, 53, § 175: virilis sexus, Pac. ap. Fest. p. 334 Müll. (Trag. Rel. p. 70 Rib.); Plin. 10, 55, 76, § 154 orbus virili sexu, Afran. ap. Fest. l. l. (Com. Rel. p. 166 Rib.): liberi sexūs virilis, Suet. Aug. 101; Front. Strat. 1, 11, 6: puberes virilis sexūs, Liv. 26, 34: tres (liberi) sexūs feminini, Suet. Calig. 7; cf. Plin. 27, 2, 2, § 4; cf.: juvenes utriusque sexūs, Suet. Aug. 31: liberi, id. ib. 100; id. Vit. 6; id. Tib. 43: sine ullo sexūs discrimine, id. Calig. 8; Tac. A. 16, 10 fin. et saep.
            Plur.: (συνεζευγμένον) jungit et diversos sexus, ut cum marem feminamque filios dicimus, Quint. 9, 3, 63: lavacra pro sexibus separavit, Spart. Hadr. 18 fin.
          2. (β) Form secus (in the poets and historians, in the latter usually virile or muliebre secus, as an acc. resp. or limiting accusative, equivalent to the genitive or ablative of quality; v. Zumpt, Lat. Gram. § 428, for the preceding virilis sexūs, the male sex): filiolam ego unam habui, Virile secus numquam ullum habui, Plaut. Rud. 1, 2, 19: virile secus, Asell. ap. Gell. 2, 13, 5: quod ejus virile secus futurum est, Varr. ib. 3, 10, 7: secus muliebre, Aus. Idyll. 11, 8: puerile, id. Epigr. 70, 6: virile ac muliebre secus populi multitudo, Sisenn. ap. Non. 222, 27: concurrentium undique virile et muliebre secus, Sall. H. Fragm. ib. 25; and in Macr. S. 2, 9 (p. 228 Gerl.): ut Philippi statuae … item majorum ejus virile ac muliebre secus omnium tollerentur, Liv 31, 44, 4: multitudinem obsessorum omnis aetatis, virile ac muliebre secus, Tac. H. 5, 13: praedas hominum virile et muliebre secus agebant, Amm. 29, 6, 8 et saep.: liberorum capitum virile secus ad decem milia capta, Liv. 26, 47, 1: athletarum spectaculo muliebre secus omnes adeo summovit, ut, etc., Suet. Aug. 44 fin.: destinatum Lacedaemoniis omnes virile secus interficere, Front. Strat. 1, 11, 6.
            Rarely as nom.: affluxere avidi talium … virile ac muliebre secus, omnis aetas, Tac. A. 4, 62: tres ordine partae, Vesta, Ceres et Juno, secus muliebre, sorores, Aus. Idyll. 11, 7; or as object of a verb: cur ex his unum secus virile designet, Arn. 1, 59; 5, 25: promiscue virile et muliebre secus trucidabant, Amm. 16, 11, 9; 27, 10, 2.
  2. II. Transf.
    1. A. A sex, of plants and minerals, Plin. 13, 4, 7, § 31; 12, 14, 32, § 61; 36, 16, 25, § 128; 36, 21, 39, § 149.
    2. B. The sexual organs, Plin. 22, 8, 9, § 20; Lact. 1, 21, 16.