Outstanding stranger in the street (7)
I believe the answer is:
salient
'outstanding' is the definition.
(I know that outstanding can be written as salient)
'stranger in the street' is the wordplay.
'stranger' becomes 'alien' (synonyms).
'in the' is an insertion indicator.
'street' becomes 'st' (abbreviation).
'alien' put into 'st' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Projecting outwards; significant" , "Foremost" , "Conspicuous; pointing outwards" , "obvious" , "Outstanding - it's lean (anag)" .)