previous vs former

previous is not a noun while former is a noun.

Word	Noun	Adjective	Verb	Adverb
previous	No	Yes	No	No
former	Yes	Yes	No	No

As adjectives, previous and former are synonyms defined as:

Other synonyms of previous include late.

previous (noun)	former (noun)
	the first of two or the first mentioned of two

previous (adjective)	former (adjective)
too soon or too hasty	referring to the first of two things or persons mentioned (or the earlier one or ones of several)
(used especially of persons) of the immediate past	belonging to the distant past
just preceding something else in time or order	belonging to some prior time
	(used especially of persons) of the immediate past