Backward rodents get the top of the bill (4)
I believe the answer is:
star
'bill' is the definition.
(thesaurus)
'backward rodents' is the wordplay.
'backward' says the letters should be written in reverse.
'rodents' becomes 'rats' (rat is a kind of rodent).
'rats' written backwards gives 'STAR'.
'get the top of the' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for star that I've seen before include "The leading player is heavenly" , "Pointed symbol" , "Glamorous celebrity" , "Heavenly body - leading actress?" , "eg The sun" .)