Lead-in to "requisite" or "K" (3)
I believe the answer is:
pre
(Other definitions for pre that I've seen before include "Before, prior to" , "Prefix meaning before" , "Combining form meaning before" , "Before or ahead of" , "Before starting" .)
I believe the answer is:
pre
(Other definitions for pre that I've seen before include "Before, prior to" , "Prefix meaning before" , "Combining form meaning before" , "Before or ahead of" , "Before starting" .)