Sanctioned Kelvin found in dictionary (4)
I believe the answer is:
'sanctioned' is the definition.
('ok' can be a synonym of 'sanction')
'kelvin found in dictionary' is the wordplay.
'kelvin' becomes 'k' ('K' can be a synonym of 'kelvin').
'found in' means one lot of letters goes inside another.
'dictionary' becomes 'oed' (Oxford English Dictionary).
'k' inserted into 'oed' is 'OKED'.
(Another definition for oked that I've seen is " Given sanction".)