Humourless after article linked to utter rat (8)
I believe the answer is:
apostate
'rat' is the definition.
(I've seen this before)
'humourless after article linked to utter' is the wordplay.
'humourless' becomes 'po' (I've seen this in other clues).
'after' is a charade indicator (letters next to each other).
'article' becomes 'a' (indefinite article).
'linked to' is a charade indicator (letters next to each other).
'utter' becomes 'state' (stating is a kind of uttering).
'po' put after 'a' is 'apo'.
'apo'+'state'='APOSTATE'
(Other definitions for apostate that I've seen before include "Religious renouncer" , "Defector" , "Dissenter" , "Deserter" , "Someone who has abandoned their religion" .)