Prominent foreigner seen in the street (7)
I believe the answer is:
salient
'prominent' is the definition.
(I know that prominent can be written as salient)
'foreigner seen in the street' is the wordplay.
'foreigner' becomes 'alien' (synonyms).
'seen in' is an insertion indicator.
'the street' becomes 'st' (abbreviation).
'alien' placed inside 'st' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Entails (anag) - most important" , "Noteworthy" , "Entails being most noticeable" , "Conspicuous; pointing outwards" , "Projecting outwards; significant" .)