Completely unfashionable - correct (8)
I believe the answer is:
outright
'completely' is the definition.
(outright means completely or totally)
'unfashionable correct' is the wordplay.
'unfashionable' becomes 'out' (similar in meaning).
'correct' becomes 'right' (right can mean correct).
'out'+'right'='OUTRIGHT'
(Other definitions for outright that I've seen before include "Directly; without reservation" , "Without reservation or stipulation" , "Completely and thoroughly" , "straight away" , "Completely - undisputed" .)