harmoniser vs intermediary

harmoniser and intermediary both are nouns.

Word	Noun	Adjective	Verb	Adverb
harmoniser	Yes	No	No	No
intermediary	Yes	No	No	No

As nouns, intermediary is a hypernym of harmoniser; that is, intermediary is a word with a broader meaning than harmoniser:

harmoniser: a mediator who brings one thing into harmonious agreement with another
intermediary: a negotiator who acts as a link between parties

Other hypernyms of harmoniser include go-between, intercessor, intermediator, mediator.

harmoniser (noun)	intermediary (noun)
a mediator who brings one thing into harmonious agreement with another	a negotiator who acts as a link between parties
a musician who sings or plays in harmony