substandard vs nonstandard

substandard and nonstandard both are adjectives.

Word	Noun	Adjective	Verb	Adverb
substandard	No	Yes	No	No
nonstandard	No	Yes	No	No

substandard (adjective)	nonstandard (adjective)
falling short of some prescribed norm	not standard; not accepted as a model of excellence
	varying from or not adhering to a standard
	not conforming to the language usage of a prestige group within a community