Silly person, the man in dress (6)
I believe the answer is:
clothe
'dress' is the definition.
('clothe' can be a synonym of 'dress')
'silly person the man' is the wordplay.
'silly person' becomes 'clot'.
'the man' becomes 'he' (**).
'clot'+'he'='CLOTHE'
'in' acts as a link.
(Other definitions for clothe that I've seen before include "robe" , "apparel" , "Fit out with garments" , "Remote area in Mongolia/China" , "Provide with garments" .)