quartet (n.)
- band
- biquadrate
- brass
- coaction
- collaboration
- collectivism
- collusion
- combo
- commensalism
- communalism
- communism
- community
- complicity
- concert
- concord
- concordance
- concurrence
- cooperation
- cooperativeness
- duet
- duo
- ecumenicalism
- ecumenicism
- ecumenism
- ensemble
- esprit
- fellowship
- four
- foursome
- group
- harmony
- morale
- mutualism
- mutuality
- octet
- orchestra
- quad
- quadrangle
- quadrature
- quadrennium
- quadrilateral
- quadrille
- quadruplet
- quatern
- quaternary
- quaternion
- quaternity
- quintet
- reciprocity
- rectangle
- septet
- sestet
- sextet
- solidarity
- square
- strings
- symbiosis
- symphony
- synergism
- synergy
- teamwork
- terzetto
- tetrad
- tetragon
- tetragram
- tetragrammaton
- tetrahedron
- tetralogy
- trio
- triumvirate
- troika
- woodwind
