retardation vs retardent

retardation and retardent both are nouns.

Word	Noun	Adjective	Verb	Adverb
retardation	Yes	No	No	No
retardent	Yes	No	No	No

As nouns, retardation and retardent are synonyms defined as:

Other synonyms of retardation include retardant.

retardation (noun)	retardent (noun)
the act of slowing down or falling behind	any agent that retards or delays or hinders
a decrease in rate of change
lack of normal development of intellectual capacities
any agent that retards or delays or hinders
the extent to which something is delayed or held back