Wicked king's not part of reason for incoherent state (6)
I believe the answer is:
sinful
'wicked' is the definition.
(synonyms)
'king's not part of reason for incoherent state' is the wordplay.
'king' becomes 'k' (abbreviation for king in chess).
'not part of' indicates named letters should be taken away.
'reason for incoherent state' becomes 'skinful' (informal term for enough alcohol to get drunk on).
'skinful' with 'k' taken out is 'SINFUL'.
(Other definitions for sinful that I've seen before include "Offensive to God" , "very unpleasant" , "Morally wrong; wicked" , "Habitually wicked" , "Wicked, unholy" .)