replacement vs novation

replacement and novation both are nouns.

Word	Noun	Adjective	Verb	Adverb
replacement	Yes	No	No	No
novation	Yes	No	No	No

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

replacement: the act of furnishing an equivalent person or thing in the place of another
novation: (law) the replacement of one obligation by another by mutual agreement of both parties; usually the replacement of one of the original parties to a contract with the consent of the remaining party

Other hyponyms of replacement include pitching change, supersedure, supersession, displacement, supplanting.

replacement (noun)	novation (noun)
the act of furnishing an equivalent person or thing in the place of another	(law) the replacement of one obligation by another by mutual agreement of both parties; usually the replacement of one of the original parties to a contract with the consent of the remaining party
a person or thing that takes or can take the place of another
an event in which one thing is substituted for another
a person who follows next in order
someone who takes the place of another person
filling again by supplying what has been used up