epicycloid vs cardioid

epicycloid and cardioid both are nouns.

Word	Noun	Adjective	Verb	Adverb
epicycloid	Yes	No	No	No
cardioid	Yes	No	No	No

As nouns, cardioid is a hyponym of epicycloid; that is, cardioid is a word with a more specific, narrower meaning than epicycloid:

epicycloid: a line generated by a point on a circle rolling around another circle
cardioid: an epicycloid in which the rolling circle equals the fixed circle

epicycloid (noun)	cardioid (noun)
a line generated by a point on a circle rolling around another circle	an epicycloid in which the rolling circle equals the fixed circle