co-occurrence vs occurrence

co-occurrence and occurrence both are nouns.

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

As nouns, occurrence is a hypernym of co-occurrence; that is, occurrence is a word with a broader meaning than co-occurrence:

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

Other hypernyms of co-occurrence include happening, natural event, occurrent.

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