repeat vs come about

repeat is a noun but come about is not a noun.

Word	Noun	Adjective	Verb	Adverb
repeat	Yes	No	Yes	No
come about	No	No	Yes	No

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

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

repeat (noun)	come about (noun)
an event that repeats

repeat (verb)	come about (verb)
happen or occur again	come to pass
to say, state, or perform again
to say again or imitate
make or do or perform again
repeat an earlier theme of a composition
do over