Some jam on going between (5)
I believe the answer is:
among
'between' is the definition.
(I've seen this before)
'some jam on going' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'AMONG' is hidden within 'jam on going'.
(Other definitions for among that I've seen before include "Amid" , "In the middle of, say a crowd" , "In the midst of (others)" , "Surrounded by" , "Within" .)