come vs come about

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

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

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

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

come (noun)	come about (noun)
the thick white fluid containing spermatozoa that is ejaculated by the male genital tract

come (verb)	come about (verb)
come to pass; arrive, as in due course	come to pass
be found or available
reach or enter a state, relation, condition, use, or position
happen as a result
have a certain priority
come to one's mind; suggest itself
move toward, travel toward something or somebody or approach something or somebody
be received
cover a certain distance
reach a destination; arrive by movement or progress
experience orgasm
come under, be classified or included
proceed or get along
extend or reach
to be the product or result
exist or occur in a certain point in a series
be a native of
to measure up to in kind or quality
add up in number or quantity
come forth
come from; be connected by a relationship of blood, for example