The Collaborative International Dictionary of English v.0.48:

Dipnoi \Dip"no*i\, n. pl. [NL., fr. Gr. ? ? with two breathing
   apertures; di- = di`s- twice + ? breath.] (Zool.)
   A group of ganoid fishes, including the living genera
   Ceratodus and Lepidosiren, which present the closest
   approximation to the Amphibia. The air bladder acts as a
   lung, and the nostrils open inside the mouth. See
   Ceratodus, and Illustration in Appendix.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Dipnoi
    n 1: bony fishes of the southern hemisphere that breathe by a
         modified air bladder as well as gills; sometimes classified
         as an order of Crossopterygii [syn: Dipnoi, subclass
         Dipnoi]