Always in culpable error (3)
I believe the answer is:
eer
'always' is the definition.
(synonyms)
'in culpable error' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EER' is hidden within 'culpable error'.
(Other definitions for eer that I've seen before include "Ever poetically" , "Ever to the poet (3)." , "Before, poetically speaking (1'2)" , "Always (poetical)" , "Always (poetic)" .)