Source : Webster's Revised Unabridged Dictionary (1913)

Supposititious \Sup*pos`i*ti"tious\, a. [L. suppositicus. See
   {Supposition}.]
   1. Fraudulently substituted for something else; not being
      what is purports to be; not genuine; spurious;
      counterfeit; as, a supposititious child; a supposititious
      writing. --Bacon.

   2. Suppositional; hypothetical. [R.] --Woodward. --
      {Sup*pos`i*ti"tious*ly}, adv. --
      {Sup*pos`i*ti"tious*ness}, n.