coincidence vs unison

coincidence and unison both are nouns.

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

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

Other hyponyms of coincidence include concomitance, overlap, contemporaneity, contemporaneousness.

coincidence (noun)	unison (noun)
the temporal property of two things happening at the same time	(music) two or more sounds or tones at the same pitch or in octaves
the quality of occupying the same position or area in space	occurring together or simultaneously
an event that might have been arranged although it was really accidental	corresponding exactly