The Collaborative International Dictionary of English v.0.48:

Portative \Por"ta*tive\, a. [Cf. F. portatif.]
   1. Portable. [Obs.]
      [1913 Webster]

   2. (Physics) Capable of holding up or carrying; as, the
      portative force of a magnet, of atmospheric pressure, or
      of capillarity.
      [1913 Webster]