Leap year, partly (6)
I believe the answer is:
spring
I believe this clue is a double definition.
'leap' is the first definition.
(leap can mean to spring or jump)
'year partly' is the second definition.
(part of the year)
(Other definitions for spring that I've seen before include "split" , "Season of growth" , "in which vegetation begins to appear" , "Spa" , "Start season" .)