retardation vs idiocy

retardation and idiocy both are nouns.

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

As nouns, idiocy is a hyponym of retardation; that is, idiocy is a word with a more specific, narrower meaning than retardation:

retardation (noun)	idiocy (noun)
the act of slowing down or falling behind	extreme mental retardation
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