The Collaborative International Dictionary of English v.0.48:

Troilus \Tro"i*lus\, n.; pl. L. Troili, E. Troiluses. [NL.,
   fr. L. Troilus, Gr. ?, the son of Priam.] (Zool.)
   A large, handsome American butterfly (Euph[oe]ades troilus,
   or Papilio troilus). It is black, with yellow marginal
   spots on the front wings, and blue spots on the rear wings;
   -- also called troilus butterfly.
   [1913 Webster]