Chinchilla or capybara (6)
I believe the answer is:
rodent
'chinchilla or capybara' is the definition.
(I know that Chinchilla laniger is a type of rodent)
This is all the clue.
(Other definitions for rodent that I've seen before include "Animal such as a mouse" , "Rat perhaps" , "Eg, mouse, squirrel" , "Small gnawing mammal" , "Vermin" .)