parlor grand piano vs parlour grand piano

parlor grand piano and parlour grand piano both are nouns.

Word	Noun	Adjective	Verb	Adverb
parlor grand piano	Yes	No	No	No
parlour grand piano	Yes	No	No	No

As nouns, parlor grand piano and parlour grand piano are synonyms defined as:

Other synonyms of parlor grand piano include baby grand, baby grand piano, parlor grand, parlour grand.

parlor grand piano (noun)	parlour grand piano (noun)
a small grand piano	a small grand piano