rhombohedron vs parallelepiped

rhombohedron and parallelepiped both are nouns.

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

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

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

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

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