deceleration vs slowing

deceleration and slowing both are nouns.

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

As nouns, deceleration and slowing are synonyms defined as:

Other synonyms of deceleration include retardation.

deceleration (noun)	slowing (noun)
the act of decelerating; decreasing the speed	a decrease in rate of change
a decrease in rate of change
(physics) a rate of decrease in velocity