The story
Formed in English as hepta- + -merous, as opposed to the apparent surface analysis of heptamer + -ous; compare the Ancient Greek ἑπτᾰμερής (heptămerḗs, “having seven parts”).
Etymology from Wiktionary, CC BY-SA 4.0.
heptamerous
Today it means: Comprising seven parts or members, as with seven petals on a flower. Full definition →