Prominent foreigner encountered in the street (7)
I believe the answer is:
salient
'prominent' is the definition.
(I know that prominent can be written as salient)
'foreigner encountered in the street' is the wordplay.
'foreigner' becomes 'alien' (synonyms).
'encountered in' is an insertion indicator.
'the street' becomes 'st' (abbreviation).
'alien' put inside 'st' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Prominent - in tales (anag)" , "Entails being most noticeable" , "obvious" , "part of defences" , "Prominent, most noticeable" .)