The Collaborative International Dictionary of English v.0.48:

Lungfish \Lung"fish`\, n. (Zool.)
   Any fish belonging to the Dipnoi; -- so called because they
   have both lungs and gills.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lungfish
    n 1: air-breathing fish having an elongated body and fleshy
         paired fins; certain species construct mucus-lined mud
         coverings in which to survive drought