Had known editor, to an extent (5)
I believe the answer is:
owned
'had' is the definition.
('own' can be a synonym of 'have')
'known editor to an extent' is the wordplay.
'to an extent' says the answer is hidden in the clue.
'OWNED' is hidden within 'known editor'.
(Other definitions for owned that I've seen before include "Had lawful title to" , "to oneself?" , "made a confession" , "Confessed" , "Possesed" .)