pub vs free house

pub and free house both are nouns.

Word	Noun	Adjective	Verb	Adverb
pub	Yes	No	No	No
free house	Yes	No	No	No

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

pub: tavern consisting of a building with a bar and public rooms; often provides light meals
free house: a public house that is not controlled by a brewery and so is free to sell different brands of beer and ale

Other hyponyms of pub include alehouse.

pub (noun)	free house (noun)
tavern consisting of a building with a bar and public rooms; often provides light meals	a public house that is not controlled by a brewery and so is free to sell different brands of beer and ale