Enthusiast embracing King as chum (6)
I believe the answer is:
friend
'chum' is the definition.
(I know that chum can be written as friend)
'enthusiast embracing king' is the wordplay.
'enthusiast' becomes 'fiend' (fiend can mean someone addicted to something).
'embracing' is an insertion indicator.
'king' becomes 'R' (abbreviation of Latin rex).
'fiend' going around 'r' is 'FRIEND'.
'as' is the link.
(Other definitions for friend that I've seen before include "Buddy, chum" , "Member of a religious community" , "Companion; Quaker" , "Buddy, mate" , "Comrade for finder" .)