"Doubt" set in quotes (8)
I believe the answer is:
question
'doubt' is the definition.
(synonyms)
'set in quotes' is the wordplay.
'set' indicates anagramming the letters (instruction to set the letters).
'in'+'quotes'='inquotes'
'inquotes' anagrammed gives 'QUESTION'.
(Other definitions for question that I've seen before include "Challenge" , "Ask; doubt" , "What could initiate this" , "dispute" , "Query" .)