Lewis & Short

ălăcer, cris, e, adj. (also in masc. alacris, Enn., v. below; Ter. Eun. 2, 3, 13, and Verg. A. 5, 380; cf. Charis. p. 63 P.
In more ancient times, alacer comm.; cf. Serv. ad Verg. A. 6, 685, and 2. acer) [perh. akin to alere = to nourish, and olēre = to grow; cf. Cic. Verr. 1, 6, 17; Auct. ad Her. 2, 19, 29], lively, brisk, quick, eager, active; glad, happy, cheerful (opp. languidus; cf. Doed. Syn. 3, 247, and 4, 450.
In the class. per., esp. in Cicero, with the access. idea of joyous activity).

  1. I. Lit.
    1. A. Of men: ignotus juvenum coetus, alternā vice Inibat alacris, Bacchio insultans modo, Enn. ap. Charis. p. 214 P.: quid tu es tristis? quidve es alacris? why are you so disturbed? or why so excited? Ter. Eun. 2, 3, 13 ( = incitatus, commotus, Ruhnk.): videbant Catilinam alacrem atque laetum, active and joyous, Cic. Mur. 24, 49: valentes imbecillum, alacres perterritum superare, id. Cael. 28: Aman laetus et alacer, Vulg. Esth. 5, 9: alacres animo sumus, are eager in mind, Cic. Fam. 5, 12 fin. Manut.; Verg. A. 6, 685 al.
      With ad: alacriores ad reliquum perficiendum, Auct. ad Her. 2, 31: ad maleficia, id. ib. 2, 30: ad bella suscipienda alacer et promptus animus, Caes. B. G. 3, 19; so Sall. C. 21, 5: ad rem gerendam, Nep. Paus. 2, 6.
      With super: alacri corde super omnibus, Vulg. 3 Reg. 8, 66.
      In Sall. once for nimble, active: cum alacribus saltu, cum velocibus cursu certabat, Fragm. 62, p. 248 Gerl.
    2. B. Of animals: equus, Cic. Div. 33, 73: bestiae, Auct. ad Her. 2, 19.
  2. II. Transf., poet., of concrete and abstract things: alacris voluptas, a lively pleasure, Verg. E. 5, 58; so, alacres enses, quick, ready to cut, Claud. Eutr. 2, 280: involant (in pugnam) impetu alacri, with a spirited, vigorous onset, Plaut. Am. 1, 1, 90.
    Sup. not used; cf. Charis. 88 P.; Rudd. I. p. 177, n. 48.
    Adv.: ălăcrĭter, briskly, eagerly, Amm. 14, 2.
    Comp., Just. 1, 6, 10.

ălăcrĭter, adv., v. alacer fin.