Wordnet 3.0
NOUN (1)
1. 
 any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs; 
[syn: sea cow, sirenian mammal, sirenian]
The Collaborative International Dictionary of English v.0.48:
Sirenian \Si*re"ni*an\, n. (Zool.)
   Any species of Sirenia.
   [1913 Webster]
WordNet (r) 3.0 (2006):
sirenian
    n 1: any of two families of large herbivorous aquatic mammals
         with paddle-shaped tails and flipper-like forelimbs and no
         hind limbs [syn: sea cow, sirenian mammal, sirenian]