Source : Webster's Revised Unabridged Dictionary (1913)

Substantival \Sub`stan*ti"val\, a.
   Of or pertaining to a substantive; of the nature of
   substantive. -- {Sub`stan*ti"val*ly}, adv.

Source : WordNet®

substantival
     adj : of or relating to or having the nature or function of a
           substantive (i.e. a noun or noun equivalent); "a
           substantival constitutent"