A joint partner (as in a business enterprise).

Roget 890: friend, friend of one's bosom; alter ego; best friend, bosom friend, soulmate, fast friend; amicus [Lat.]; usque ad aras [Lat.]; fidus Achates [Lat.]; persona grata.    acquaintance, neighbor, next-door neighbor, casual acquaintance, nodding acquaintance; wellwisher.    favorer, fautor^†, patron, Mecaenas; tutelary saint, good genius, advocate, partisan, sympathizer; ally; friend in need etc. (auxiliary) 711.    comrade, mate, companion, familiar, confrere, comrade, camarade^†, confidante, intimate; old crony, crony; chum; pal; buddy, bosom buddy; playfellow, playmate, childhood friend; bedfellow, bedmate; chamber fellow.    associate, colleague, compeer.    schoolmate, schoolfellow^†; classfellow^†, classman^†, classmate; roommate; fellow-man, stable companion.    best man, maid of honor, matron of honor.    compatriot; fellow countryman, countryman.    shopmate, fellow-worker, shipmate, messmate^†; fellow companion, boon companion, pot companion; copartner, partner, senior partner, junior partner.    Arcades ambo Pylades and Orestes Castor and Arcades ambo Pylades and Orestes Castor and Pollux^†, Nisus and Euryalus [Lat.], Damon and Pythias, par nobile fratrum [Lat.].    host, Amphitryon^†, Boniface; guest, visitor, prot_eg_e.    ... show more