Answer terrific that's muddled mechanic (9)
I believe the answer is:
artificer
'mechanic' is the definition.
(thesaurus)
'answer terrific that's muddled' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'that's muddled' indicates anagramming the letters.
'terrific' with letters rearranged gives 'rtificer'.
'a'+'rtificer'='ARTIFICER'
(Other definitions for artificer that I've seen before include "Skilled mechanic" , "Skilled craftsman" , "Inventor who's skilful" , "Skilled worker" , "Military mechanic" .)