trip vs happen

trip is a noun but happen is not a noun.

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

trip (noun)	happen (noun)
a journey for some purpose (usually including the return)
an unintentional but embarrassing blunder
a light or nimble tread
a catch mechanism that acts as a switch
an accidental misstep threatening (or causing) a fall
an exciting or stimulating experience
a hallucinatory experience induced by drugs

trip (verb)	happen (verb)
get high, stoned, or drugged	come to pass
put in motion or move to act	come into being; become reality
miss a step and fall or nearly fall	happen, occur, or be the case in the course of events or by chance
cause to stumble	come upon, as if by accident; meet with
make a trip for pleasure	chance to be or do something, without intention or causation