Certain to jump (5)
I believe the answer is:
bound
I believe this clue is a double definition.
'certain' is the first definition.
(as in the phrase 'it's bound to be')
'jump' is the second definition.
(I know that bound is a type of jump)
'to' acts as a link.
(Other definitions for bound that I've seen before include "fixed a > limit" , "Obliged; leap" , "upward jump" , "long jump" , "demarcation" .)