Garment a foot short kept in vessel (6)
I believe the answer is:
caftan
'garment' is the definition.
(caftan is a kind of garment)
'a foot short kept in vessel' is the wordplay.
'foot short' becomes 'ft' (abbreviation for 'foot').
'kept in' indicates putting letters inside.
'vessel' becomes 'can' (I've seen this before).
'a'+'ft'='aft'
'aft' going inside 'can' is 'CAFTAN'.
(Other definitions for caftan that I've seen before include "Type of long dress with wide sleeves" , "Long cloak-like garment with sleeves" , "Shirt" , "Middle-Eastern long dress" , "Cotton or silk ankle-length garment with full sleeves worn by men in the Levant" .)