Unable to speak about fashionable time (6)
I believe the answer is:
minute
'time' is the definition.
(I've seen this before)
'unable to speak about fashionable' is the wordplay.
'unable to speak' becomes 'mute' (I've seen this before).
'about' indicates putting letters inside.
'fashionable' becomes 'in' (similar in meaning).
'mute' going around 'in' is 'MINUTE'.
(Other definitions for minute that I've seen before include "Extremely small" , "Little -- 60 18 across" , "Brief note" , "Tiny; period of time" , "Tiny like time unit (6)" .)