ground floor vs first floor

ground floor and first floor both are nouns.

Word	Noun	Adjective	Verb	Adverb
ground floor	Yes	No	No	No
first floor	Yes	No	No	No

As nouns, ground floor and first floor are synonyms defined as:

ground floor and first floor: the floor of a building that is at or nearest to the level of the ground around the building

Other synonyms of ground floor include ground level.

ground floor (noun)	first floor (noun)
the floor of a building that is at or nearest to the level of the ground around the building	the floor of a building that is at or nearest to the level of the ground around the building
becoming part of a venture at the beginning (regarded as position of advantage)