The Oxford Thesaurus An A-Z Dictionary of Synonyms - allyn.

1) comrade, confederate, collaborator, coadjutor; accessory, accomplice; associate, partner, friend: I had hoped to have you as an ally in my proposal for reorganization. The Allies finally defeated the Nazi war machine in 1945. --v. 2) league, combine, unite, join (up) , team (up) , side, band together, associate, affiliate, collaborate, confederate: In their attempt at a take-over of our company, the raiders have allied themselves with two banks. We shall ally the Romans to us and conquer the territory.