agreement vs unison

agreement and unison both are nouns.

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

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

agreement (noun)	unison (noun)
compatibility of observations	(music) two or more sounds or tones at the same pitch or in octaves
the thing arranged or agreed to	occurring together or simultaneously
the verbal act of agreeing	corresponding exactly
the statement (oral or written) of an exchange of promises
the determination of grammatical inflection on the basis of word relations
harmony of people's opinions or actions or characters