1. (n.) Mutual action and reaction; mutual privilege or favor\.

2. (n.) Reciprocal advantages, obligations, or rights; reciprocation.

accord accordance affinity agape agreement alternation amity balance battledore and shuttlecock bipartisanship bonds of harmony brotherly love caritas cement of friendship charity coaction coadjuvancy coadministration coagency cochairmanship codirectorship coequality collaboration collaborativeness collectivism collusion commensalism common effort common enterprise communalism communion communism communitarianism community community of interests commutation compatibility complicity concert concord concordance concurrence congeniality cooperation cooperativeness corelation correlation correlativism correlativity correspondence counterchange cross fire duet duumvirate ecumenicalism ecumenicism ecumenism empathy equilibrium equipollence equivalence esprit esprit de corps exchange feeling of identity fellow feeling fellowship frictionlessness give-and-take good vibes good vibrations happy family harmony identity interchange intermutation interplay inverse proportion inverse ratio inverse relationship joining of forces joint effort joint operation kinship lex talionis like-mindedness love mass action measure for measure morale mutual admiration mutual assistance mutual support mutual transfer mutualism mutuality octet oneness peace permutation pooling pooling of resources proportionality pulling together quartet quid pro quo quintet rapport rapprochement reciprocality reciprocation relativity retaliation septet sextet sharing solidarity something for something symbiosis symmetry sympathy symphony synergism synergy team spirit teamwork tit for tat transposal transposition trio triumvirate troika understanding union unison united action unity