fallacious vs unsound

fallacious and unsound both are adjectives.

Word	Noun	Adjective	Verb	Adverb
fallacious	No	Yes	No	No
unsound	No	Yes	No	No

As adjectives, fallacious and unsound are synonyms defined as:

fallacious (adjective)	unsound (adjective)
involving deception	not sound financially
based on an incorrect or misleading notion or information	not in good condition; damaged or decayed
containing or based on a fallacy	suffering from severe mental illness
	containing or based on a fallacy
	physically unsound or diseased
	of e.g. advice