Unfashionable lot had reformed (3,3)
I believe the answer is:
old hat
'unfashionable' is the definition.
('old-hat' can be similar in meaning to 'unfashionable')
'lot had reformed' is the wordplay.
'reformed' indicates anagramming the letters.
'lot'+'had'='lothad'
'lothad' anagrammed gives 'OLD-HAT'.
(Other definitions for old hat that I've seen before include "Out of date thing" , "Familiar for too long" , "A tediously familiar thing" , "Shabby cover" , "Tediously familiar or outdated, like obsolete headgear" .)