all right vs OK

all right is not a noun while OK is a noun.

Word	Noun	Adjective	Verb	Adverb
all right	No	Yes	No	Yes
OK	Yes	No	No	Yes

As adverbs, all right and OK are synonyms defined as:

all right and OK: an expression of agreement normally occurring at the beginning of a sentence

Other synonyms of all right include alright, fine, very well.

all right (noun)	OK (noun)
	an endorsement
	a state in south central United States

all right (adjective)	OK (adjective)
being satisfactory or in satisfactory condition

all right (adverb)	OK (adverb)
an expression of agreement normally occurring at the beginning of a sentence	an expression of agreement normally occurring at the beginning of a sentence
without doubt (used to reinforce an assertion)
in a satisfactory or adequate manner