mansion vs mansion house

mansion and mansion house both are nouns.

Word	Noun	Adjective	Verb	Adverb
mansion	Yes	No	No	No
mansion house	Yes	No	No	No

As nouns, mansion and mansion house are synonyms defined as:

Other synonyms of mansion include hall, manse, residence.

mansion (noun)	mansion house (noun)
a large and imposing house	a large and imposing house
(astrology) one of 12 equal areas into which the zodiac is divided