retention vs retain

retention is a noun but retain is not a noun.

Word	Noun	Adjective	Verb	Adverb
retention	Yes	No	No	No
retain	No	No	Yes	No

retention (noun)	retain (noun)
the act of retaining something
the power of retaining liquid
the power of retaining and recalling past experience

retention (verb)	retain (verb)
	keep in one's mind
	secure and keep for possible future use or application
	allow to remain in a place or position or maintain a property or feature
	hold back within