recoil vs happen

recoil is a noun but happen is not a noun.

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

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

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

recoil (noun)	happen (noun)
a movement back from an impact
the backward jerk of a gun when it is fired

recoil (verb)	happen (verb)
spring back, as from a forceful thrust	come to pass
draw back, as with fear or pain	come into being; become reality
spring back; spring away from an impact	happen, occur, or be the case in the course of events or by chance
come back to the originator of an action with an undesired effect	come upon, as if by accident; meet with
	chance to be or do something, without intention or causation