cymatium vs cyma recta

cymatium and cyma recta both are nouns.

Word	Noun	Adjective	Verb	Adverb
cymatium	Yes	No	No	No
cyma recta	Yes	No	No	No

As nouns, cyma recta is a hyponym of cymatium; that is, cyma recta is a word with a more specific, narrower meaning than cymatium:

cymatium: (architecture) a molding for a cornice; in profile it is shaped like an S (partly concave and partly convex)
cyma recta: a cyma in which the upper section is concave and the lower section is convex

Other hyponyms of cymatium include cyma reversa, ogee.

cymatium (noun)	cyma recta (noun)
(architecture) a molding for a cornice; in profile it is shaped like an S (partly concave and partly convex)	a cyma in which the upper section is concave and the lower section is convex