"... should the __ arise" (4)

I believe the answer is:
need
(Other definitions for need that I've seen before include "What's lacking" , "Shortage" , "Lack or require" , "A condition" , "Want - require(ment)" .)
I believe the answer is:
need
(Other definitions for need that I've seen before include "What's lacking" , "Shortage" , "Lack or require" , "A condition" , "Want - require(ment)" .)