retard vs decrease

retard and decrease both are nouns.

Word	Noun	Adjective	Verb	Adverb
retard	Yes	No	Yes	No
decrease	Yes	No	Yes	No

As verbs, decrease is a hypernym of retard; that is, decrease is a word with a broader meaning than retard:

Other hypernyms of retard include diminish, fall, lessen.

retard (noun)	decrease (noun)
a person of subnormal intelligence	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

retard (verb)	decrease (verb)
lose velocity; move more slowly	decrease in size, extent, or range
cause to move more slowly or operate at a slower rate	make become smaller
slow the growth or development of
be delayed