Nonad is a see also of polyad.
As nouns the difference between nonad and polyad
is that nonad
is a collection, or series of nine things while polyad
is a group consisting of an indeterminate number of things or people.
a collection, or series of nine things
*True nonads seem to be rare. Most collections of nine things are actually triads of triads.
*Also the name of a photographic filter used for astronomy, meaning "no Sodium D-line", where Sodium has the symbol Na, from the Latin natrium .
* See also