lengthening vs prolongation

lengthening and prolongation both are nouns.

Word	Noun	Adjective	Verb	Adverb
lengthening	Yes	No	No	No
prolongation	Yes	No	No	No

As nouns, lengthening and prolongation are synonyms defined as:

Other synonyms of lengthening include perpetuation, protraction.

lengthening (noun)	prolongation (noun)
the act of prolonging something	the act of prolonging something
	amount or degree or range to which something extends
	the consequence of being lengthened in duration