Webster’s Revised Unabridged Dictionary · 1913
Implausible
Im·plau′si·ble (ĭm·pla̤′zĭ·b'l), a. [Pref. im- not + plausible: cf. F. implausible.] Not plausible; not wearing the appearance of truth or credibility, and not likely to be believed. "Implausible harangues." Swift.
— Im·plau′si·ble·ness, n. — Im·plau′si·bly, adv.