Lewis & Short

concŭbĭtus, ūs, m. [concubo].

  1. I. A lying together; in gen. (very rare), for sleeping. Varr. L. L. 7, § 78 Müll.; at dinner, reclining, Prop. 4 (5), 8, 36 (cf. concubo, I.): dentium, a firm, close shutting together of the teeth, Cael. Aur. Acut. 2, 10; 3, 6.
    Far more freq.,
  2. II. Copulation, coition (in sing. and plur.): ficti (deorum) cum humano genere concubitus, Cic. N. D. 1, 16, 42; so Liv. 4, 2, 6; Ov. M. 4, 207; 6, 541 al.; * Hor. A. P. 398; Suet. Aug. 94; id. Tib. 44: concubitusque tuos furtim, Tib. 2, 5, 53.
    Of animals, Verg. E. 6, 50; id. G. 3, 130; Col. 8, 15, 7 al.