Mid 17th century (in an earlier sense). From classical Latin partiārius sharing or participating, associate, joint, held jointly or in common, shared, in post-classical Latin also as noun, land-tenant at a share of the crop, co-participant from parti-, alternative stem of part-, pars + -ārius. Compare Middle French partiaire (adjective) sharing gains and losses with another, especially in land tenure, (noun) tenant sharing his gains with his landlord, Old Occitan parcier, Spanish parcero, now aparcero (937 as parcera), Catalan parcer, Portuguese parceiro, Italian parziario.