Earliest (5)
'earliest' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for first that I've seen before include "second to none" , "In winning position" , "higher than the others" , "Rifts of supreme sort" , "Pre-eminent" .)
'earliest' is the definition.
(synonyms)
This is all the clue.
(Other definitions for soonest that I've seen before include "At the earliest time" , "As early as possible" , "'Least said, ... mended (7)'" , "First" , "Most readily" .)