negotiate vs mediate

negotiate is not an adjective while mediate is an adjective.

Word	Noun	Adjective	Verb	Adverb
negotiate	No	No	Yes	No
mediate	No	Yes	Yes	No

As verbs, mediate is a hyponym of negotiate; that is, mediate is a word with a more specific, narrower meaning than negotiate:

Other hyponyms of negotiate include arbitrate, intercede, intermediate, liaise, renegociate, renegotiate, bargain, dicker, broker.

negotiate (adjective)	mediate (adjective)
	acting through or dependent on an intervening agency
	being neither at the beginning nor at the end in a series

negotiate (verb)	mediate (verb)
discuss the terms of an arrangement	act between parties with a view to reconciling differences
succeed in passing through, around, or over	occupy an intermediate or middle position or form a connecting link or stage between two others