Huge body placed on vessel (6)
I believe the answer is:
saturn
'huge body' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'placed on vessel' is the wordplay.
'placed' becomes 'sat' (sitting is a kind of placing).
'on' says to put letters next to each other.
'vessel' becomes 'urn' (urn is a kind of vessel).
'sat'+'urn'='SATURN'
Can you help me to learn more?
(Other definitions for saturn that I've seen before include "space traveller" , "Giant planet" , "Titan its moon" , "orbits the sun" , "Roman god - gas giant" .)