Octad

Part of speech: noun

Pronunciation: /ˈɒktæd/

Definitions

1. A group or series of eight things, or a chemical element having a valence of eight
2. A structure or arrangement comprising eight individual parts or components, which can apply to both numerical sequences and certain scientific contexts
3. A collection or assembly consisting of eight entities, often used in mathematics and chemistry to describe specific groupings or characteristics of elements

Etymology: "Octad" is a plain formation: "oct-", from the Greek "okto" meaning eight, combined with "-ad", a suffix used in English to form nouns denoting a group or set, as in "triad" (three) and "dyad" (two). Put together, the word simply means a set of eight, following the same pattern that gives us "monad" for a single unit and "decad" for ten. The "-ad" ending comes from the Greek "-as" (genitive "-ados"), which marks a unit or a collection, and English borrowed the pattern through Latin and into scientific and mathematical vocabulary. Because the suffix is productive, coinages like "octad" are easy to build from number prefixes, which is why the word reads at once as a count rather than an idiom.

Synonyms: eight, octet