The Collaborative International Dictionary of English v.0.48:

Fer-de-lance \Fer`-de-lance"\, n. [F., the iron of a lance,
   lance head.] (Zool.)
   A large, venomous serpent (Trigonocephalus lanceolatus) of
   Brazil and the West Indies. It is allied to the rattlesnake,
   but has no rattle.
   [1913 Webster]