retardation vs deceleration

retardation and deceleration both are nouns.

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

As nouns, retardation and deceleration are synonyms defined as:

Other synonyms of retardation include slowing.

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