An opponent of the Yemen perhaps (5)
I believe the answer is:
enemy
'an opponent' is the definition.
(I know that enemy is a type of opponent)
'yemen perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'yemen' is an anagram of 'ENEMY'.
'of the' is the link.
(Other definitions for enemy that I've seen before include "is against us" , "Opposing force" , "Antagonist" , "other side (like 16)" , "Armed adversary" .)