Etymon in a sentence as a noun

That invites the thought that the joke was just that and outweighed the etymon.

"septante", "octante", "nonante" would be coherently based on Latin etymons, but if you want to coherently use "heptante", which relies on a Greek etymon, you should probably also use "ennéante" in lieu of "nonante".

Etymon definitions

noun

a simple form inferred as the common basis from which related words in several languages can be derived by linguistic processes

See also: root