Criticise the one taking a nostrum (7)
I believe the answer is:
panacea
'nostrum' is the definition.
(synonyms)
'criticise the one taking a' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'the one' becomes 'ace' (ace has a value of one in some card games).
'taking' is a charade indicator (letters next to each other).
'pan'+'ace'+'a'='PANACEA'
(Other definitions for panacea that I've seen before include "Hypothetical universal remedy" , "that's going to help a lot" , "universal solution" , "Nostrum" , "offering solution to all ills" .)