Grand rite, perhaps, slowing down (9)
I believe the answer is:
retarding
'slowing down' is the definition.
('retard' can be a synonym of 'slow down')
'grand rite perhaps' is the wordplay.
'perhaps' indicates an anagram.
'grand'+'rite'='grandrite'
'grandrite' is an anagram of 'RETARDING'.
(Another definition for retarding that I've seen is " causing delay".)
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