Lewis & Short

1. rēgŭlus, i, m. dim. [rex].

  1. I. The ruler of a small country (Gr. δυνάστης), a petty king, prince, chieftain, lord (freq. in the historians; not in Cæs. or Cic.): regulos se acceptos in fidem in Hispaniā reges reliquisse, Liv. 37, 25; Sall. J. 11, 2; Liv. 5, 38; 27, 4; 29, 4 al.: Cilicum reguli, Tac. A. 2, 80; id. Agr. 24; Suet. Calig. 5; Vulg. Josue, 13, 3 al.
  2. II. Transf.
    1. A. Of the king-bee, Varr. R. R. 3, 16, 18.
    2. B. A king’s son, a prince (cf. rex and regina), Liv. 42, 24, 10; 45, 14, 6 al.
    3. C. A small bird, Auct. Carm. Phil. 13.
    4. D. A kind of serpent, Hier. in Isa. 16, 59, 6; Vulg. Prov. 23, 32; id. Isa. 30, 6.