Nonadic is a derived term of nonad.
As a noun nonad
is a collection, or series of nine things.
As an adjective nonadic is
of or pertaining to an nonad; ninefold.
Other Comparisons: What's the difference?
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 .
of or pertaining to an nonad; ninefold
*This word has been coined by allusion to tetradic, octadic etc, but has little usage.