delay vs retardation

delay and retardation both are nouns.

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

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

delay: the act of delaying; inactivity resulting in something being put off until a later time
retardation: the act of slowing down or falling behind

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

Other hyponyms of delay include extension, moratorium.

delay (noun)	retardation (noun)
the act of delaying; inactivity resulting in something being put off until a later time	the act of slowing down or falling behind
time during which some action is awaited	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

delay (verb)	retardation (verb)
cause to be slowed down or delayed
stop or halt
slow the growth or development of
act later than planned, scheduled, or required