In a flash, one bit endlessly fractured (11)
I believe the answer is:
fashionable
'in' is the definition.
('fashionable' can be similar in meaning to 'in')
'a flash one bit endlessly fractured' is the wordplay.
'endlessly' means to remove the last letter.
'fractured' indicates anagramming the letters.
'a'+'flash'+'one'+'bit'='aflashonebit'
'aflashonebit' with its final letter taken off is 'aflashonebi'.
'aflashonebi' anagrammed gives 'FASHIONABLE'.
(Other definitions for fashionable that I've seen before include "Modish" , "Trendy" , "A la mode" , "What's in" .)