see vs come across

see is a noun but come across is not a noun.

Word	Noun	Adjective	Verb	Adverb
see	Yes	No	Yes	No
come across	No	No	Yes	No

As verbs, see and come across are synonyms defined as:

Other synonyms of see include encounter, meet, run across, run into.

see (noun)	come across (noun)
the seat within a bishop's diocese where his cathedral is located

see (verb)	come across (verb)
deem to be	be received or understood
perceive (an idea or situation) mentally	communicate the intended meaning or impression
get to know or become aware of, usually accidentally	come together
be careful or certain to do something; make certain of something	be perceived in a certain way; make a certain impression
deliberate or decide	find unexpectedly
make sense of; assign a meaning to
find out, learn, or determine with certainty, usually by making an inquiry or other effort
match or meet
receive as a specified guest
imagine; conceive of; see in one's mind
come together
conduct someone someplace
perceive by sight or have the power to perceive by sight
perceive or be contemporaneous with
see or watch
see and understand, have a good eye
observe as if with an eye
undergo or live through a difficult experience
observe, check out, and look over carefully or inspect
date regularly; have a steady relationship with
go to see a place, as for entertainment
go to see for professional or business reasons
go to see for a social visit
take charge of or deal with