Unacceptable to suppress current belief (6)
I believe the answer is:
notion
'belief' is the definition.
('notion' can be a synonym of 'belief')
'unacceptable to suppress current' is the wordplay.
'unacceptable' becomes 'noton' (I've seen this before).
'to suppress' indicates putting letters inside.
'current' becomes 'i' (symbol for electric current).
'noton' placed around 'i' is 'NOTION'.
(Other definitions for notion that I've seen before include "Idea or whim" , "Whim or fancy" , "Vague understanding" , "Concept, belief" , "A vague and possibly incorrect opinion" .)