Hamster or capybara (6)
I believe the answer is:
rodent
'hamster or capybara' is the definition.
(I know that hamster is a type of rodent)
This is all the clue.
(Other definitions for rodent that I've seen before include "Eg, mouse, squirrel" , "Mouse or squirrel, say" , "Mouse maybe" , "Animal such as a mouse" , "Small gnawing mammal" .)