Step round vermin (4)
I believe the answer is:
pest
'vermin' is the definition.
'step round' is the wordplay.
'round' is an anagram indicator.
'step' with letters rearranged gives 'PEST'.
(Other definitions for pest that I've seen before include "Destructive creature" , "Nuisance; half a European capital" , "Constant nuisance" , "Infernal nuisance" , "Annoying thing" .)