Before, prior to (3)
I believe the answer is:
pre
I believe this clue is a double definition.
'before' is the first definition.
(prefix meaning 'before')
'prior to' is the second definition.
(I've seen this in another clue)
(Other definitions for pre that I've seen before include "Before starting" , "Combining form meaning before" , "Prefix meaning before" , "Before, prior to" , "Before or ahead of" .)