Flash wearing leather in street (7)
I believe the answer is:
instant
'flash' is the definition.
(synonyms)
'wearing leather in street' is the wordplay.
'wearing' becomes 'in' (you are 'in' the clothes you're wearing).
'leather' becomes 'tan' (tan can mean to convert into leather).
'in' means one lot of letters goes inside another.
'street' becomes 'st' (abbreviation).
'tan' put within 'st' is 'stant'.
'in'+'stant'='INSTANT'
(Other definitions for instant that I've seen before include "A second - coffee, maybe" , "Occurring immediately, like some fast food" , "Fast, flash" , "type of coffee" , "Occurring with no delay" .)