Formerly in older style (4)
I believe the answer is:
erst
'formerly' is the definition.
(I've seen this before)
'in older style' is the wordplay.
'in' says the answer is hidden in the clue.
'ERST' is hidden in the letters of 'older style'.
(Other definitions for erst that I've seen before include "in the past" , "Rest turned formerly" , "At first; formerly" , "in former times" .)