Run away to join up perhaps (5)
I believe the answer is:
elope
'run away' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for elope that I've seen before include "Run away to Gretna Green?" , "Run away with lover" , "Do a runner" , "Run away to get married" , "Run away together" .)