first vs foremost

first is a noun but foremost is not a noun.

Word	Noun	Adjective	Verb	Adverb
first	Yes	Yes	No	Yes
foremost	No	Yes	No	Yes

As adjectives, first and foremost are synonyms defined as:

Other synonyms of first include world-class.

As adverbs, first and foremost are synonyms defined as:

Other synonyms of first include first of all, first off, firstly.

As adverbs, first and foremost are synonyms defined as:

first (noun)	foremost (noun)
the fielding position of the player on a baseball team who is stationed at first of the bases in the infield (counting counterclockwise from home plate)
the lowest forward gear ratio in the gear box of a motor vehicle; used to start a car moving
an honours degree of the highest class
the first element in a countable series
the first or highest in an ordering or series
the time at which something is supposed to begin

first (adjective)	foremost (adjective)
preceding all others in time or space or degree	ranking above all others
highest in pitch or chief among parts or voices or instruments or orchestra sections	situated closest to the bow
ranking above all others	preceding all others in spatial position
serving to begin
serving to set in motion

first (adverb)	foremost (adverb)
before anything else	prominently forward
prominently forward	before anything else
the initial time
before another in time, space, or importance