Award most agreeable old canon set up (8)
I believe the answer is:
bestowal
'award' is the definition.
(I've seen this in another clue)
'most agreeable old canon set up' is the wordplay.
'most agreeable' becomes 'best'.
'old' becomes 'o' (abbreviation).
'canon' becomes 'law' (canon can mean a law or principle).
'set up' is a reversal indicator (in a down clue, letters go up).
'law' written backwards gives 'wal'.
'best'+'o'+'wal'='BESTOWAL'
(Other definitions for bestowal that I've seen before include "presentation" , "Conferment (of an honour)" , "Act of giving" , "Act of conferring (eg, grant on someone)" , "award" .)