preposterous vs idiotic

preposterous and idiotic both are adjectives.

Word	Noun	Adjective	Verb	Adverb
preposterous	No	Yes	No	No
idiotic	No	Yes	No	No

As adjectives, preposterous and idiotic are synonyms defined as:

Other synonyms of preposterous include absurd, cockeyed, derisory, laughable, ludicrous, nonsensical, ridiculous.

preposterous (adjective)	idiotic (adjective)
so unreasonable as to invite derision	so unreasonable as to invite derision
	insanely irresponsible
	having a mental age of three to seven years