Neil returns with a stranger (5)
I believe the answer is:
alien
'stranger' is the definition.
(synonyms)
'neil returns with a' is the wordplay.
'returns' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'neil' written backwards gives 'lien'.
'lien' put after 'a' is 'ALIEN'.
(Other definitions for alien that I've seen before include "24a [ESTRANGE]" , "Outlandish" , "Foreign, strange" , "Foreigner, outsider" , "Foreign; extraterrestrial" .)