Trespasser (8)
I believe the answer is:
intruder
'trespasser' is the definition.
(I know that trespasser can be written as intruder)
This is the entire clue.
(Other definitions for intruder that I've seen before include "One making uninvited entry" , "I'd return (anag.)" , "Person who enters uninvited, perhaps a burglar" , "Housebreaker" , "Uninvited and unwelcome visitor" .)