retentivity vs retentive

retentivity is a noun but retentive is not a noun.

Word	Noun	Adjective	Verb	Adverb
retentivity	Yes	No	No	No
retentive	No	Yes	No	No

retentivity (noun)	retentive (noun)
the power of retaining liquid
the property of retaining possessions that have been acquired
the power of retaining and recalling past experience

retentivity (adjective)	retentive (adjective)
	good at remembering
	having the capacity to retain something
	having the power, capacity, or quality of retaining water