Haunt lake isle wearing spotless uniform (7)
I believe the answer is:
purlieu
'haunt' is the definition.
(thesaurus)
'lake isle wearing spotless uniform' is the wordplay.
'lake' becomes 'l'.
'isle' becomes 'i'.
'wearing' means one lot of letters goes inside another.
'spotless' becomes 'pure'.
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'l'+'i'='li'
'li' inserted into 'pure' is 'purlie'.
'purlie'+'u'='PURLIEU'
(Other definitions for purlieu that I've seen before include "Border" , "City's outlying district" , "Land bordering a forest still subject to forest laws" , "Person's usual haunts" , "One's limits or usual haunts" .)