Important stranger in street (7)
I believe the answer is:
salient
'important' is the definition.
(thesaurus)
'stranger in street' is the wordplay.
'stranger' becomes 'alien' ('alien' can be a synonym of 'stranger').
'in' indicates putting letters inside.
'street' becomes 'st'.
'alien' put into 'st' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Entails being most noticeable" , "Noteworthy" , "defence work" , "Leaping (heraldry)" , "Outstanding - it's lean (anag)" .)