Army poet’s sleeveless jacket (6)
I believe the answer is:
tabard
'sleeveless jacket' is the definition.
(I've seen this before)
'army poet's' is the wordplay.
'army' becomes 'TA' (abbreviation for Territorial Army).
'poet' becomes 'bard' (bard is a kind of poet).
'ta'+'bard'='TABARD'
(Other definitions for tabard that I've seen before include "Sleeveless jerkin" , "[A] top" , "Short tunic, open at the sides" , "Herald's coat or tunic" , "Jacket worn by a herald" .)