Nice chap conceals weapon in clothing (7)
I believe the answer is:
garment
'clothing' is the definition.
(I know that clothing can be written as garment)
'nice chap conceals weapon' is the wordplay.
'nice chap' becomes 'gent' (a gentleman).
'conceals' indicates putting letters inside.
'weapon' becomes 'arm' (synonyms).
'gent' enclosing 'arm' is 'GARMENT'.
'in' acts as a link.
(Other definitions for garment that I've seen before include "Perhaps shift" , "Something put on" , "Singular outfit" , "Item of clothing" , "Article of dress" .)