regal vs imperial

regal is not a noun while imperial is a noun.

Word	Noun	Adjective	Verb	Adverb
regal	No	Yes	No	No
imperial	Yes	Yes	No	No

As adjectives, regal and imperial are synonyms defined as:

Other synonyms of regal include majestic, purple, royal.

regal (noun)	imperial (noun)
	a piece of luggage carried on top of a coach
	a small tufted beard worn by Emperor Napoleon III

regal (adjective)	imperial (adjective)
belonging to or befitting a supreme ruler	befitting or belonging to an emperor or empress
	relating to or associated with an empire
	of or belonging to the British Imperial System of weights and measures
	belonging to or befitting a supreme ruler