Complexity confounded any critic (9)
I believe the answer is:
intricacy
'complexity' is the definition.
(intricacy is a kind of complexity)
'confounded any critic' is the wordplay.
'confounded' indicates anagramming the letters.
'any'+'critic'='anycritic'
'anycritic' anagrammed gives 'INTRICACY'.
(Other definitions for intricacy that I've seen before include "Detailed complexity" , "Complication" , "Complexity of detail" .)