Son initially has no trousers (6)
I believe the answer is:
slacks
'trousers' is the definition.
(type of trousers)
'son initially has no' is the wordplay.
'initially' indicates taking the first letters.
'has no' becomes 'lacks'.
The first letter of 'son' is 's'.
's'+'lacks'='SLACKS'
(Other definitions for slacks that I've seen before include "Avoids work - trousers" , "bags" , "casual attire" , "Works lazily; trousers" , "takes it easy" .)