Plural of epeidon; the plural form referring to a type of geometric or structural element, particularly in crystallography or architecture.
From Greek 'epi' (upon) + possibly 'hedon' (seat or base). This is a technical term with uncertain etymology, primarily used in specialized scientific literature.
Though rarely used today, 'epeidia' appears in vintage crystallography texts where it described specific plane arrangements in crystal structures before modern terminology took over!
Complete word intelligence in one call. Free tier — 50 lookups/day.