1 Achates, alter ego, boon companion, bosom friend, buddy (informal) china (Brit. slang) chum (informal) cock (Brit. informal) companion, comrade, confidant, crony, familiar, homeboy (slang, chiefly U.S.) intimate, mate (informal) pal, partner, playmate, soul mate
2 adherent, advocate, ally, associate, backer, benefactor, partisan, patron, protagonist, supporter, well-wisher
Antonyms
adversary, antagonist, competitor, enemy, foe, opponent, rival