space cadet vs simpleton

space cadet and simpleton both are nouns.

Word	Noun	Adjective	Verb	Adverb
space cadet	Yes	No	No	No
simpleton	Yes	No	No	No

As nouns, simpleton is a hypernym of space cadet; that is, simpleton is a word with a broader meaning than space cadet:

space cadet: someone who seems unable to respond appropriately to reality (as if under the influence of some narcotic drug)
simpleton: a person lacking intelligence or common sense

Other hypernyms of space cadet include simple.

space cadet (noun)	simpleton (noun)
someone who seems unable to respond appropriately to reality (as if under the influence of some narcotic drug)	a person lacking intelligence or common sense