country house vs villa

country house and villa both are nouns.

Word	Noun	Adjective	Verb	Adverb
country house	Yes	No	No	No
villa	Yes	No	No	No

As nouns, villa is a hyponym of country house; that is, villa is a word with a more specific, narrower meaning than country house:

country house: a house (usually large and impressive) on an estate in the country
villa: pretentious and luxurious country residence with extensive grounds

Other hyponyms of country house include chateau, dacha, shooting box, shooting lodge, summer house.

country house (noun)	villa (noun)
a house (usually large and impressive) on an estate in the country	pretentious and luxurious country residence with extensive grounds
	country house in ancient Rome consisting of residential quarters and farm buildings around a courtyard
	detached or semidetached suburban house