trigger vs occur

trigger is a noun but occur is not a noun.

Word	Noun	Adjective	Verb	Adverb
trigger	Yes	No	Yes	No
occur	No	No	Yes	No

trigger (noun)	occur (noun)
an act that sets in motion some course of events
lever that activates the firing mechanism of a gun
a device that activates or releases or causes something to happen

trigger (verb)	occur (verb)
release or pull the trigger on	come to pass
put in motion or move to act	come to one's mind; suggest itself
	to be found to exist