semidetached house vs duplex house

semidetached house and duplex house both are nouns.

Word	Noun	Adjective	Verb	Adverb
semidetached house	Yes	No	No	No
duplex house	Yes	No	No	No

As nouns, semidetached house and duplex house are synonyms defined as:

semidetached house and duplex house: a house with two units sharing a common wall

Other synonyms of semidetached house include duplex.

semidetached house (noun)	duplex house (noun)
a house with two units sharing a common wall	a house with two units sharing a common wall