co-occurrence vs concomitant

co-occurrence and concomitant both are nouns.

Word	Noun	Adjective	Verb	Adverb
co-occurrence	Yes	No	No	No
concomitant	Yes	Yes	No	No

As nouns, co-occurrence and concomitant are synonyms defined as:

co-occurrence and concomitant: an event or situation that happens at the same time as or in connection with another

Other synonyms of co-occurrence include accompaniment, attendant.

co-occurrence (noun)	concomitant (noun)
the temporal property of two things happening at the same time	an event or situation that happens at the same time as or in connection with another
an event or situation that happens at the same time as or in connection with another

co-occurrence (adjective)	concomitant (adjective)
	occurring with or following as a consequence