The Collaborative International Dictionary of English v.0.48:

Assumptive \As*sump"tive\, a. [L. assumptivus, fr. assumptus,
   fr. assumere.]
   Assumed, or capable of being assumed; characterized by
   assumption; making unwarranted claims. -- As*sump"tive*ly,
   adv.
   [1913 Webster]

   Assumptive arms (Her.), originally, arms which a person had
      a right to assume, in consequence of an exploit; now,
      those assumed without sanction of the Heralds' College.
      --Percy Smith.
      [1913 Webster]