Nutria (5)
I believe the answer is:
coypu
'nutria' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for coypu that I've seen before include "Beaver lookalike" , "Large South American aquatic rodent" , "Beaver-like creature" , "rodents" , "South American rodent bred for its fur, nutria" .)