Source : Webster's Revised Unabridged Dictionary (1913)

Swordtail \Sword"tail`\, n. (Zo["o]l.)
   (a) The limulus.
   (b) Any hemipterous insect of the genus {Uroxiphus}, found
       upon forest trees.

Source : WordNet®

swordtail
     n : freshwater fish of Central America having a long swordlike
         tail; popular aquarium fish [syn: {helleri}, {topminnow},
          {Xyphophorus helleri}]