The Collaborative International Dictionary of English v.0.48:

Septet \Sep*tet"\, Septette \Sep*tette"\, n. [From L. septem
   seven, like duet, from L. duo.]
   1. A set of seven persons or objects; as, a septet of
      singers.
      [1913 Webster]

   2. (Mus.) A musical composition for seven instruments or
      seven voices; -- called also septuor.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Septuor \Sep"tu*or\, n. [F.] (Mus.)
   A septet.
   [1913 Webster]