simple vs dim-witted

simple is a noun but dim-witted is not a noun.

Word	Noun	Adjective	Verb	Adverb
simple	Yes	Yes	No	No
dim-witted	No	Yes	No	No

As adjectives, simple and dim-witted are synonyms defined as:

Other synonyms of simple include simple-minded.

simple (noun)	dim-witted (noun)
a person lacking intelligence or common sense
any herbaceous plant having medicinal properties

simple (adjective)	dim-witted (adjective)
(botany) of leaf shapes; of leaves having no divisions or subdivisions	lacking mental capacity and subtlety
having few parts; not complex or complicated or involved
easy and not involved or complicated
exhibiting childlike simplicity and credulity
unornamented
lacking mental capacity and subtlety
apart from anything else; without additions or modifications