deceleration vs retardation

deceleration and retardation both are nouns.

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

As nouns, deceleration and retardation are synonyms defined as:

Other synonyms of deceleration include slowing.

deceleration (noun)	retardation (noun)
the act of decelerating; decreasing the speed	the act of slowing down or falling behind
a decrease in rate of change	a decrease in rate of change
(physics) a rate of decrease in velocity	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