decelerate vs slow

decelerate is not an adjective while slow is an adjective.

Word	Noun	Adjective	Verb	Adverb
decelerate	No	No	Yes	No
slow	No	Yes	Yes	Yes

As verbs, decelerate and slow are synonyms defined as:

Other synonyms of decelerate include retard, slow down, slow up.

As verbs, slow is a hyponym of decelerate; that is, slow is a word with a more specific, narrower meaning than decelerate:

Other hyponyms of decelerate include slow down, slow up, delay, detain, hold up.

decelerate (adjective)	slow (adjective)
	not moving quickly; taking a comparatively long time
	at a slow tempo
	(used of timepieces) indicating a time earlier than the correct time
	(of business) not active or brisk
	slow to learn or understand; lacking intellectual acuity
	so lacking in interest as to cause mental weariness

decelerate (verb)	slow (verb)
lose velocity; move more slowly	lose velocity; move more slowly
reduce the speed of	become slow or slower
	cause to proceed more slowly

decelerate (adverb)	slow (adverb)
	without speed (`slow' is sometimes used informally for `slowly')
	showing a time that is earlier than the actual time