come across vs encounter

come across is not a noun while encounter is a noun.

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

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

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

come across (noun)	encounter (noun)
	a minor short-term fight
	a casual meeting with a person or thing
	a hostile disagreement face-to-face
	a casual or unexpected convergence

come across (verb)	encounter (verb)
be received or understood	contend against an opponent in a sport, game, or battle
communicate the intended meaning or impression	come together
come together	come upon, as if by accident; meet with
be perceived in a certain way; make a certain impression	be beset by
find unexpectedly	experience as a reaction