1 sharer, partaker, associate, colleague, participant, accomplice, accessory, confederate, comrade, ally, collaborator, companion, team-mate, fellow, alter ego, friend, Colloq pal, sidekick, mate, US and Canadian buddy, cohort:
His partner in the bank robbery was arrested this morning.
2 wife or husband, spouse, mate, helpmate, helpmeet, consort:
She became my life partner more than 50 years ago.
3 companion, fellow-dancer:
Won't you change partners and dance with me?