The way in which something is done (6)
I believe the answer is:
manner
'the way in which something is done' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for manner that I've seen before include "Way in which something is done" , "Demeanour" , "Fashion, style" , "Style, air" , "Bearing; style of art" .)