D defs.my
Entry 2 senses Webster, 1913

Octad

· Oc·tad · IPA /ˈɑkˌtæd/
01 n. An atom or radical which has a valence of eight, or is octavalent.
  1. 1.
    An atom or radical which has a valence of eight, or is octavalent.(Chem.)
  2. 2.
    A group of eight things.