ally ally /ˈælaɪ/

noun

1. () A friendly nation  ( ally )
   a friendly nation
   
2. () An associate who provides cooperation or assistance  ( ally , friend )
   an associate who provides cooperation or assistance
    He's a good ally in fight
   he's a good ally in fight
   
   

verb

1. Become an ally or associate, as by a treaty or marriage  ( ally )
   become an ally or associate, as by a treaty or marriage
    He allied himself with the Communists
   He allied himself with the Communists