Come out east to join up (6)
I believe the answer is:
emerge
'come out' is the definition.
('emerge' can be a synonym of 'come out')
'east to join up' is the wordplay.
'east' becomes 'e' ('E' can be a synonym of 'east').
'to join up' becomes 'merge'.
'e'+'merge'='EMERGE'
(Other definitions for emerge that I've seen before include "Come into view" , "Develop" , "Come out or transpire" , "Emanate" , "Come into greater prominence" .)