I will leave banlieue swirling in clouds (7)
I believe the answer is:
nebulae
'clouds' is the definition.
(I've seen this before)
'i will leave banlieue swirling' is the wordplay.
'will leave' indicates named letters should be taken away.
'swirling' indicates an anagram (letters get swirled around).
'banlieue' with 'i' removed is 'banleue'.
'banleue' anagrammed gives 'NEBULAE'.
'in' acts as a link.
(Other definitions for nebulae that I've seen before include "Bright patches in sky from distant galaxies" , "Stardust" , "Gas or dust clouds in space" , "Cloud-like patches in space" , "where stars are born" .)