Complete one sort of clue correctly (9)
I believe the answer is:
downright
'complete' is the definition.
(similar in meaning)
'one sort of clue correctly' is the wordplay.
'one sort of clue' becomes 'down' (as opposed to an across clue).
'correctly' becomes 'right' (synonyms).
'down'+'right'='DOWNRIGHT'
(Other definitions for downright that I've seen before include "Completely" , "rank" , "Out-and-out" , "Utter, complete" , "Frank" .)