fallacious
[adjective]
Synonyms: illogical, invalid, irrational, mad, nonrational, reasonless, sophistic, unreasonable, unreasoned, misleading, beguiling, deceiving, deceptive, deluding, delusive, delusory, false

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Antonyms: sound, valid, veritable

[TahlilGaran] English Synonym Dictionary ▲

fal‧la‧cious /fəˈleɪʃəs/ adjective formal
containing or based on false ideas:
Such an argument is misleading, if not wholly fallacious.
—fallaciously adverb

[TahlilGaran] Dictionary of Contemporary English ▲