The Collaborative International Dictionary of English v.0.48:
Fallacious \Fal*la"cious\, a. [L. fallaciosus, fr. fallacia: cf. F. fallacieux. See Fallacy.] Embodying or pertaining to a fallacy; illogical; fitted to deceive; misleading; delusive; as, fallacious arguments or reasoning. -- Fal*la"cious*ly, adv. -Fal*la"cious*ness, n. [1913 Webster]