The Collaborative International Dictionary of English v.0.48:

octet \oc*tet"\, n. [From L. octo eight, like E. duet, fr.L.
   duo. See Octave.]
   1. (Mus.) A composition for eight parts, usually for eight
      solo instruments or voices.
      [1913 Webster]

   2. A group of eight singers or eight musicians.
      [PJC]

WordNet (r) 3.0 (2006):

octet
    n 1: the cardinal number that is the sum of seven and one [syn:
         eight, 8, VIII, eighter, eighter from Decatur,
         octad, ogdoad, octonary, octet]
    2: eight performers or singers who perform together [syn:
       octet, octette]
    3: a set of eight similar things considered as a unit [syn:
       octet, octette]
    4: eight people considered as a unit [syn: octet, octette,
       eightsome]
    5: a musical composition written for eight performers [syn:
       octet, octette]

The Free On-line Dictionary of Computing (19 January 2023):

octet

    Eight bits.  This term is used in
   networking, in preference to byte, because some systems use
   the term "byte" for things that are not 8 bits long.

   (1995-03-03)