Source : Webster's Revised Unabridged Dictionary (1913)

Lungfish \Lung"fish`\, n. (Zo["o]l.)
   Any fish belonging to the Dipnoi; -- so called because they
   have both lungs and gills.

Source : WordNet®

lungfish
     n : air-breathing fish having an elongated body and fleshy
         paired fins; certain species construct mucus-lined mud
         coverings in which to survive drought
     [also: {lungfishes} (pl)]