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]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "octet":
   Octateuch, Spenserian stanza, antistrophe, beta particle,
   bipartisanship, book, burden, canto, cathode particle, chorus,
   coaction, coadjuvancy, coadministration, coagency, cochairmanship,
   codirectorship, collaboration, collaborativeness, collectivism,
   collusion, commensalism, common effort, common enterprise,
   communalism, communism, communitarianism, community, complicity,
   concert, concord, concordance, concurrence, cooperation,
   cooperativeness, couplet, distich, duet, duettino, duo, duumvirate,
   ecumenicalism, ecumenicism, ecumenism, eight, eighter from Decatur,
   electron, electron affinity, electron cloud, electron pair,
   electron shells, electron spin, electron transfer,
   electron-positron pair, energy level, ensemble music,
   ensemble singing, envoi, epode, esprit, esprit de corps,
   excited state, extranuclear electrons, fellow feeling, fellowship,
   ground state, harmony, heptastich, hexastich, joining of forces,
   joint effort, joint operation, line, lone pair, mass action,
   measure, monostich, morale, mutual assistance, mutualism,
   mutuality, negatron, octad, octagon, octahedron, octameter,
   octastich, octastyle, octave, octavo, octonary, octosyllable,
   ogdoad, orbital electron, ottava rima, part music, part singing,
   part song, pentastich, photoelectron, polyphonic music, pooling,
   pooling of resources, pulling together, quartet, quatrain, quintet,
   reciprocity, recoil electron, refrain, rhyme royal,
   secondary electron, septet, septuor, sestet, sextet, shared pair,
   solidarity, stanza, stave, strain, strophe, subvalent electrons,
   surface-bound electron, syllable, symbiosis, synergism, synergy,
   team spirit, teamwork, tercet, terza rima, terzet, terzetto,
   tetrastich, thermion, trio, triplet, tristich, triumvirate, troika,
   united action, utas, valence electrons, valence shell, verse,
   wandering electron



The Free On-line Dictionary of Computing (30 December 2018):

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)