rhombohedron vs parallelopiped

rhombohedron and parallelopiped both are nouns.

Word	Noun	Adjective	Verb	Adverb
rhombohedron	Yes	No	No	No
parallelopiped	Yes	No	No	No

As nouns, parallelopiped is a hypernym of rhombohedron; that is, parallelopiped is a word with a broader meaning than rhombohedron:

rhombohedron: a parallelepiped bounded by six similar faces (either rhombuses or parallelograms)
parallelopiped: a prism whose bases are parallelograms

Other hypernyms of rhombohedron include parallelepiped, parallelepipedon, parallelopipedon, hexahedron.

rhombohedron (noun)	parallelopiped (noun)
a parallelepiped bounded by six similar faces (either rhombuses or parallelograms)	a prism whose bases are parallelograms