Welcoming arrangement of opus, one he composed (4,5)
I believe the answer is:
open house
'welcoming arrangement' is the definition.
The definition and answer can be both groups as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'opus one he composed' is the wordplay.
'composed' indicates an anagram.
'opus'+'one'+'he'='opusonehe'
'opusonehe' anagrammed gives 'OPEN HOUSE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for open house that I've seen before include "Hospitality to all comers - unlock doors?" , "welcoming situation" , "Hospitality to all comers at home" , "Invitation to all" , "catering for all" .)