mediation vs intercession

mediation and intercession both are nouns.

Word	Noun	Adjective	Verb	Adverb
mediation	Yes	No	No	No
intercession	Yes	No	No	No

As nouns, intercession is a hypernym of mediation; that is, intercession is a word with a broader meaning than mediation:

mediation: the act of intervening for the purpose of bringing about a settlement
intercession: the act of intervening (as to mediate a dispute, etc.)

Other hypernyms of mediation include intervention.

mediation (noun)	intercession (noun)
the act of intervening for the purpose of bringing about a settlement	the act of intervening (as to mediate a dispute, etc.)
a negotiation to resolve differences that is conducted by some impartial party	a prayer to God on behalf of another person