(n.) A composition for two performers, whether vocal or instrumental\.

bipartisanship both brace coaction coadjuvancy coadministration coagency cochairmanship codirectorship collaboration collaborativeness collectivism collusion commensalism common effort common enterprise communalism communism communitarianism community complicity concert concord concordance concurrence cooperation cooperativeness couple couplet distich double harness doublet duad duettino duo duumvirate dyad ecumenicalism ecumenicism ecumenism ensemble music ensemble singing esprit esprit de corps fellow feeling fellowship harmony joining of forces joint effort joint operation mass action match mates morale mutual assistance mutualism mutuality octet pair part music part singing part song polyphonic music pooling pooling of resources pulling together quartet quintet reciprocity septet septuor sestet set of two sextet solidarity span symbiosis synergism synergy team team spirit teamwork terzet terzetto the two trio triumvirate troika twain two twosome united action yoke