A worn vessel, I see (5)
I believe the answer is:
tunic
'a worn' is the definition.
I can't tell whether this definition defines the answer.
'vessel i see' is the wordplay.
'vessel' becomes 'tun' (type of vessel for beer).
'see' becomes 'C' (the word for the letter, according to Chambers).
'tun'+'i'+'c'='TUNIC'
Can you help me to learn more?
(Other definitions for tunic that I've seen before include "Knee-length cloak" , "Jacket of some soldiers" , "Upper garment, for a soldier say" , "Belted coat" , "Partly uniform" .)