Lewis & Short

1. orca, ae, f. [cf. ἄρχα],

  1. I. a kind of whale, an orc, Plin. 9, 6, 5, § 12.
  2. II. Transf.
    1. A. A large-bellied vessel, a butt, tun (cf.: seria, dolium): orca genus marinae beluae maximum dicitur: ad cujus similitudinem vasa quoque ficaria orcae dicunter: sunt enim teretes, atque uniformi specie, Fest. p. 180 Müll.: orcae in Hispaniā fervore musti ruptae, Varr. R. R. 1, 13, 6; Col. 12, 15, 2: Byzantia orca (which had contained pickled tunny-fish), Hor. S. 2, 4, 66; cf. Pers. 3, 76.
    2. B. A tunnel used for throwing dice, a dice-box: angusta, Pers. 3, 50: interim dum contemplor orcam, taxillos perdidi, Pompon. ap. Prisc. p. 615 P. (Com. Rel. p. 214 Rib.).