brighten vs clear

brighten is not a noun while clear is a noun.

Word	Noun	Adjective	Verb	Adverb
brighten	No	No	Yes	No
clear	Yes	Yes	Yes	Yes

As verbs, brighten and clear are synonyms defined as:

Other synonyms of brighten include clear up, light up.

brighten (noun)	clear (noun)
	a clear or unobstructed space or expanse of land or water
	the state of being free of suspicion

brighten (adjective)	clear (adjective)
	readily apparent to the mind
	allowing light to pass through
	free from clouds or mist or haze
	accurately stated or described
	free from confusion or doubt
	characterized by ease and quickness in perceiving
	clear and distinct to the senses; easily perceptible
	freed from any question of guilt
	easily deciphered
	clear of charges or deductions
	free from flaw or blemish or impurity
	(especially of a title) free from any encumbrance or limitation that presents a question of fact or law
	affording free passage or view
	free of restrictions or qualifications
	characterized by freedom from troubling thoughts (especially guilt)
	(of sound or color) free from anything that dulls or dims
	free from contact or proximity or connection

brighten (verb)	clear (verb)
make more cheerful through the use of color	remove
become clear	rid of obstructions
	make clear, bright, light, or translucent
	free (the throat) by making a rasping sound
	make a way or path by removing objects
	remove the occupants of
	remove (people) from a building
	rid of instructions or data
	make free from confusion or ambiguity; make clear
	pronounce not guilty of criminal charges
	grant authorization or clearance for
	settle, as of a debt
	pass by, over, or under without making contact
	pass an inspection or receive authorization
	go away or disappear
	earn on some commercial or business transaction; earn as salary or wages
	yield as a net profit
	make as a net profit
	be debited and credited to the proper bank accounts
	sell to get rid of
	clear from impurities, blemishes, pollution, etc.
	free from payment of customs duties, as of a shipment
	go unchallenged; be approved
	become clear

brighten (adverb)	clear (adverb)
	in an easily perceptible manner
	entirely