come vs happen

come is a noun but happen is not a noun.

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

As verbs, happen is a hypernym of come; that is, happen is a word with a broader meaning than come:

Other hypernyms of come include come about, fall out, go on, hap, occur, pass, pass off, take place.

come (noun)	happen (noun)
the thick white fluid containing spermatozoa that is ejaculated by the male genital tract

come (verb)	happen (verb)
come to pass; arrive, as in due course	come to pass
be found or available	come into being; become reality
reach or enter a state, relation, condition, use, or position	happen, occur, or be the case in the course of events or by chance
happen as a result	come upon, as if by accident; meet with
have a certain priority	chance to be or do something, without intention or causation
come to one's mind; suggest itself
move toward, travel toward something or somebody or approach something or somebody
be received
cover a certain distance
reach a destination; arrive by movement or progress
experience orgasm
come under, be classified or included
proceed or get along
extend or reach
to be the product or result
exist or occur in a certain point in a series
be a native of
to measure up to in kind or quality
add up in number or quantity
come forth
come from; be connected by a relationship of blood, for example