Lewis & Short

ăvis, is, f. (abl. sing. avi and ave; cf. Varr. L. L. 8, § 66 Müll.; Prisc. p. 765 P.; Rhem. Palaem. p. 1374 P.; Neue, Formenl. I. pp. 218, 222; in the lang. of religion, the form avi is most common; v. infra) [cf. Sanscr. vā (which may imply av), to blow (to wave); vis, a bird; Zend, vi; with which Curt. compares οἰ-ωνός, a large bird, and Benfey αἰ-ετός, an eagle].

  1. I. Lit., a bird; or collect., the winged tribe: Liber captivos avis ferae consimilis est, Plaut. Capt. 1, 2, 7: videmus novis avibus canere undique silvas, Lucr. 1, 256: arguta, Prop. 1, 18, 30: istā enim avi (sc. aquilā) volat nulla vehementius, Cic. Div. 2, 70, 144: ave ad perfugia litorum tendente, Plin. 10, 3, 3, § 9; Vulg. Gen. 1, 2; ib. Deut. 4, 17; ib. Marc. 4, 32; ib. Luc. 13, 34 et saep.
    In Varr. once of bees: de incredibili earum avium naturā audi, Varr. R. R. 3, 16, 3.
    A description of birds is found ap. Plin. lib. 10; of their habits, ap. Varr. R. R. 3, 3 sq. and ap. Col. 8, 1 sq.
  2. II. Transf.
    1. A. Esp., in reference to auguries, since the Romans took their omens or auguries from birds (v. augurium and auspicium): post quam avem aspexit templo Anchises, Naev. ap. Prob. ad Verg. E. 6, 31.
      Hence, avis, meton., = omen a sign, omen, portent, freq. with the epithets bona, mala, sinistra ( = bona; v. sinister), adversa, etc.: liquido exeo foras Auspicio avi sinistrā, Plaut. Ep. 2, 2, 2: ducam legiones meas Avi sinistrā, auspicio liquido atque ex sententiā, id. Ps. 2, 4, 72: solvere secundo rumore aversāque avi, poët. ap. Cic. Div. 1, 16, 29, where B. and K. read adversā: malā ducis avi domum, with a bad omen, Hor. C. 1, 15, 5: este bonis avibus visi natoque mihique, Ov. F. 1, 513; so id. M. 15, 640: di, qui secundis avibus in proelium miserint, Liv. 6, 12, 9: Quā ego hunc amorem mihi esse avi dicam datum? Plaut. Cas. 3, 4, 26: Hac veniat natalis avi, Tib. 2, 2, 21.
      In abl., form ave: tunc ave deceptus falsā, Ov. M. 5, 147.
    2. B. Comically, for a man in the garb of a bird: Sed quae nam illaec est avis, quae huc cum tunicis advenit? Plaut. Poen. 5, 2, 15.
    3. C. Avis alba, v. albus, I. B. 3. e.