Sewer scurrier (3)
I believe the answer is:
rat
'sewer scurrier' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rat that I've seen before include "Desert - rodent" , "Treacherous rodent" , "shopper" , "Despicable person" , "Destructive rodent" .)