Ringo at once adjusted embracing grand group (12)
I believe the answer is:
congregation
'group' is the definition.
(congregation is a kind of group)
'ringo at once adjusted embracing grand' is the wordplay.
'adjusted' indicates anagramming the letters.
'embracing' is an insertion indicator.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'ringo'+'at'+'once'='ringoatonce'
'ringoatonce' anagrammed gives 'conregation'.
'conregation' going around 'g' is 'CONGREGATION'.
(Other definitions for congregation that I've seen before include "Group assembling for worship" , "Group of worshippers" .)