rock brake vs cliff brake

rock brake and cliff brake both are nouns.

Word	Noun	Adjective	Verb	Adverb
rock brake	Yes	No	No	No
cliff brake	Yes	No	No	No

As nouns, rock brake and cliff brake are synonyms defined as:

rock brake and cliff brake: any of several small lithophytic ferns of tropical and warm temperate regions

Other synonyms of rock brake include cliff-brake.

rock brake (noun)	cliff brake (noun)
chiefly lithophytic or epiphytic fern of North America and east Asia	any of several small lithophytic ferns of tropical and warm temperate regions
dwarf deciduous lithophytic ferns
any of several small lithophytic ferns of tropical and warm temperate regions