accident vs occurrence

accident and occurrence both are nouns.

Word	Noun	Adjective	Verb	Adverb
accident	Yes	No	No	No
occurrence	Yes	No	No	No

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

accident: anything that happens suddenly or by chance without an apparent cause
occurrence: an event that happens

Other hypernyms of accident include happening, natural event, occurrent.

accident (noun)	occurrence (noun)
anything that happens suddenly or by chance without an apparent cause	an event that happens
an unfortunate mishap; especially one causing damage or injury	an instance of something occurring