happenstance vs accident

happenstance and accident both are nouns.

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

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

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

Other hypernyms of happenstance include chance event, fortuity, stroke.

happenstance (noun)	accident (noun)
an event that might have been arranged although it was really accidental	anything that happens suddenly or by chance without an apparent cause
	an unfortunate mishap; especially one causing damage or injury