Lewis & Short

căvus, a, um, adj. [root κυ-, κυέω, to swell, etc.; cf.: κοῖλος, κενός], hollow, excavated, concave (opp. plenus, full, round; class.).

  1. I. Prop.: cava conveniant plenis, Lucr. 6, 1085: cicutae, id. 5, 1383: tibia, id. 2, 620: concha, Verg. A. 6, 171: aes, id. ib. 3, 240: testudo, id. G. 4, 464; Hor. Epod. 14, 11: bucina, Ov. M. 1, 335 et saep.: ungula, Enn. Ann. 419 Vahl.: fornaces, Lucr. 7, 202: montes, id. 5, 955: specus, Enn. Ann. 420 Vahl.: cavernae, Verg. A. 2, 53: trabs, id. ib. 3, 191 et saep.: trunci, Hor. C. 2, 19, 12: ilex, id. Epod. 16, 47: saxa, id. C. 3, 13, 14 et saep.: vena, the hollow vein, Cic. N. D. 2, 55, 138: nubes, Lucr. 6, 127; 6, 176; 6, 272; Verg. A. 1, 516; 5, 810 al.
    Hence also of a darkness enveloping one as a cloud: umbra, Verg. A. 2, 360: flumina, the deepchannelled mountain streams, id. G. 1, 326; 4, 427; cf. Luc. 1, 396: luna, waning (cf. cavo), Plin. 8, 54, 80, § 215.
    1. B. Subst.: căvum, i, n. (access. form căvus, i, m. (sc. locus), Varr. R. R. 3, 15, 1; Hor. S. 2, 6, 116; id. Ep. 1, 7, 33; Phaedr. 4, 6, 3; Col. 12, 8), a hollow, cavity, hole, Cato, R. R. 128; Plaut. Men. 1, 2, 49; Lucr. 5, 1382; Liv. 24, 34, 9; Verg. G. 1, 184; Hor. S. 2, 3, 173; Plin. 2, 79, 81, § 192; 11, 51, 112, § 266 et saep.: cava caeli, Enn. Trag. 131 Vahl.; cf.: cava caerula, id. ib. 332 Vahl.; hence, căvum aedĭum (contr. căvae-dĭum, Phn. Ep. 2, 17, 5), the inner court of Roman houses (cf. Vitr. 6, 3 Schneid.; O. Müll. Etrusk. 1, p. 255, and Archaeol. § 293, III.), Varr. L. L. 5, § 161; Vitr. 6, 3; Dict. of Antiq.
  2. II. In late Lat., trop.: menses, which have only 30 days (opp. menses pleni, which have 31 days), Censor. 20.
        1. b. = inanis, vain, empty: gloria, Paul. Nol. Carm. 22, 139: opes, id. ib. 21, 912.