Of an argument: Not according to the art of Logic; not deduced by logical methods from accepted premisses, but derived from authority or testimony…

spec. Not in accordance with rule or reason; not correctly deduced or inferred.

Impaired or spoiled by some fault, flaw, blemish, or defect; faulty, defective, imperfect, bad; corrupt, impure, debased. Logic. Of arguments, etc.

(un-, prefix1 affix 1.)

Characterized by or involving paralogism or false reasoning; illogical or unreasonable.

Characterized by or involving false reasoning; fallacious.

Logically inadmissible or illegitimate.

Of, relating to, or characterized by paralogism; = paralogical, adj.