Apron worn in companionable relationship (9)
I believe the answer is:
matrimony
'relationship' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'apron worn in companionable' is the wordplay.
'apron' becomes 'rim' (both can mean something's edge).
'worn' becomes 'on' (as in having clothes on).
'in' is an insertion indicator.
'companionable' becomes 'maty' (I can't explain this - if you can you should believe this answer much more).
'rim'+'on'='rimon'
'rimon' inserted within 'maty' is 'MATRIMONY'.
Can you help me to learn more?
(Other definitions for matrimony that I've seen before include "The state of wedlock" , "State of being married" , "wedding ceremony" , "Nuptials" .)