Squadron leader has no casual wear (6)
I believe the answer is:
slacks
'casual wear' is the definition.
(I've seen this in another clue)
'squadron leader has no' is the wordplay.
'leader' suggests taking the first letters.
'has no' becomes 'lacks'.
The first letter of 'squadron' is 's'.
's'+'lacks'='SLACKS'
(Other definitions for slacks that I've seen before include "casual attire" , "Loose casual trousers" , "Pants for casual wear" , "bags" , "takes it easy" .)