Deity had a session on a burial vessel (6)
I believe the answer is:
saturn
'deity' is the definition.
(I know that Saturn is a Roman deity)
'had a session on a burial vessel' is the wordplay.
'had a session' becomes 'sat' (I've seen this in another clue).
'on' says to put letters next to each other.
'a burial vessel' becomes 'urn' (I can't justify this - if you can you should give a lot more credence to this answer).
'sat'+'urn'='SATURN'
Can you help me to learn more?
(Other definitions for saturn that I've seen before include "Sixth planet from the sun" , "Solar system planet" , "space traveller" , "Giant planet" , "Turn as a planet" .)