The Collaborative International Dictionary of English v.0.48:

cutlass fish \cutlass fish\, cutlassfish \cutlassfish\n.
   1. (Zool.) a peculiar, long, thin, marine fish (Trichiurus
      lepturus) of the southern United States and West Indies,
      having a long whiplike scaleless body and sharp daggerlike
      teeth; -- called also frostfish, saber fish, silver
      eel, and, improperly, swordfish; also, several related
      members of the genus Trichiurus. It is closely related
      to snake mackerel.

   Syn: frost fish, frostfish, hairtail.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

cutlassfish
    n 1: long-bodied marine fishes having a long whiplike scaleless
         body and sharp teeth; closely related to snake mackerel
         [syn: cutlassfish, frost fish, hairtail]