accident vs coincidence

accident and coincidence both are nouns.

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

As nouns, coincidence is a hyponym of accident; that is, coincidence is a word with a more specific, narrower meaning than accident:

accident: anything that happens suddenly or by chance without an apparent cause
coincidence: an event that might have been arranged although it was really accidental

Other hyponyms of accident include hap, break, good luck, happy chance, happenstance, lottery.

accident (noun)	coincidence (noun)
anything that happens suddenly or by chance without an apparent cause	the temporal property of two things happening at the same time
an unfortunate mishap; especially one causing damage or injury	the quality of occupying the same position or area in space
	an event that might have been arranged although it was really accidental