happen vs effect

happen is not a noun while effect is a noun.

Word	Noun	Adjective	Verb	Adverb
happen	No	No	Yes	No
effect	Yes	No	Yes	No

happen (noun)	effect (noun)
	an outward appearance
	(of a law) having legal validity
	an impression (especially one that is artificial or contrived)
	the central meaning or theme of a speech or literary work
	a phenomenon that follows and is caused by some previous phenomenon
	a symptom caused by an illness or a drug

happen (verb)	effect (verb)
come to pass	produce
come into being; become reality	act so as to bring into existence
happen, occur, or be the case in the course of events or by chance
come upon, as if by accident; meet with
chance to be or do something, without intention or causation