Synonyms for Septet (same or very similar meaning)
WordNet sense 1 (the cardinal number that is the sum of six and one):
seven, heptad, sevener, VII, septenaryWordNet sense 2 (seven performers or singers who perform together):
septetteWordNet sense 3 (seven people considered as a unit):
sevensomeFrom the ODE community, based on WordNetadd/edit