Mate has 3 going in both directions (4)
I believe the answer is:
oppo
'mate' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for oppo that I've seen before include "Counterpart; rival" , "China" , "Opposite number (colloq.)" , "Colleague, friend (colloq.)" , "Mate" .)