Bound to start (4)
I believe the answer is:
jump
I believe this clue is a double definition.
'bound' is the first definition.
(thesaurus)
'start' is the second definition.
(jumping is a kind of starting)
'to' acts as a link.
(Other definitions for jump that I've seen before include "Suddenly increase" , "Leap (high, long or triple)" , "Hurdle" , "Vault, bound" , "Attack" .)