orchid cactus vs epiphyllum

orchid cactus and epiphyllum both are nouns.

Word	Noun	Adjective	Verb	Adverb
orchid cactus	Yes	No	No	No
epiphyllum	Yes	No	No	No

As nouns, orchid cactus and epiphyllum are synonyms defined as:

orchid cactus and epiphyllum: any cactus of the genus Epiphyllum having flattened jointed irregularly branching stems and showy tubular flowers

orchid cactus (noun)	epiphyllum (noun)
any cactus of the genus Epiphyllum having flattened jointed irregularly branching stems and showy tubular flowers	any cactus of the genus Epiphyllum having flattened jointed irregularly branching stems and showy tubular flowers