\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.