successor vs replacement

successor and replacement both are nouns.

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

As nouns, replacement is a hypernym of successor; that is, replacement is a word with a broader meaning than successor:

Other hypernyms of successor include substitute.

As nouns, successor and replacement are synonyms defined as:

successor (noun)	replacement (noun)
a thing or person that immediately replaces something or someone	the act of furnishing an equivalent person or thing in the place of another
a person who inherits some title or office	a person or thing that takes or can take the place of another
a person who follows next in order	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