Spy name attached to ancient vessel (4)
I believe the answer is:
nark
'spy' is the definition.
(I've seen this before)
'name attached to ancient vessel' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'attached to' means one lot of letters go next to another.
'ancient vessel' becomes 'ark' (ark is a kind of vessel. I am not sure about the 'ancient' bit.).
'n'+'ark'='NARK'
Can you help me to learn more?
(Other definitions for nark that I've seen before include "Annoy; police informer" , "Cause minor annoyance" , "upset" , "Stool pigeon" , "Grass; irritate" .)