Soonest (8)
I believe the answer is:
earliest
'soonest' is the definition.
(I know that soonest can be written as earliest)
This is the entire clue.
(Other definitions for earliest that I've seen before include "Arriving first" , "Original or most previous" , "Very first in a sterile manner" , "Nearest the beginning in time" , "Ateliers (anag.)" .)