repeat vs happen

repeat is a noun but happen is not a noun.

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

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

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

repeat (noun)	happen (noun)
an event that repeats

repeat (verb)	happen (verb)
happen or occur again	come to pass
to say, state, or perform again	come into being; become reality
to say again or imitate	happen, occur, or be the case in the course of events or by chance
make or do or perform again	come upon, as if by accident; meet with
repeat an earlier theme of a composition	chance to be or do something, without intention or causation
do over