The Collaborative International Dictionary of English v.0.48:

Specious \Spe"cious\, a. [L. speciosusgood-looking, beautiful,
   specious, fr. species look, show, appearance; cf. F.
   sp['e]coeux. See Species.]
   1. Presenting a pleasing appearance; pleasing in form or
      look; showy.
      [1913 Webster]

            Some [serpents] specious and beautiful to the eye.
                                                  --Bp.
                                                  Richardson.
      [1913 Webster]

            The rest, far greater part,
            Will deem in outward rites and specious forms
            Religion satisfied.                   --Milton.
      [1913 Webster]

   2. Apparently right; superficially fair, just, or correct,
      but not so in reality; appearing well at first view;
      plausible; as, specious reasoning; a specious argument.
      [1913 Webster]

            Misled for a moment by the specious names of
            religion, liberty, and property.      --Macaulay.
      [1913 Webster]

            In consequence of their greater command of specious
            expression.                           --J. Morley.
      [1913 Webster]

   Syn: Plausible; showy; ostensible; colorable; feasible. See
        Plausible.
        [1913 Webster] -- Spe"xious*ly, adv. --
        Spe"cious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

specious
    adj 1: plausible but false; "a specious claim"; "spurious
           inferences" [syn: specious, spurious]
    2: based on pretense; deceptively pleasing; "the gilded and
       perfumed but inwardly rotten nobility"; "meretricious
       praise"; "a meretricious argument" [syn: gilded,
       meretricious, specious]