The Collaborative International Dictionary of English v.0.48:

Presumptive \Pre*sump"tive\, a. [Cf. F. pr['e]somptif.]
   1. Based on presumption or probability; grounded on probable
      evidence; probable; as, presumptive proof.
      [1913 Webster]

   2. Presumptuous; arrogant. [R.] --Sir T. Browne.
      [1913 Webster]

   Presumptive evidence (Law), that which is derived from
      circumstances which necessarily or usually attend a fact,
      as distinct from direct evidence or positive proof;
      indirect or circumstantial evidence. "Presumptive evidence
      of felony should be cautiously admitted." --Blackstone.
      The distinction, however, between direct and presumptive
      (or circumstantial) evidence is now generally abandoned;
      all evidence being now more or less direct and more or
      less presumptive.

   Presumptive heir. See Heir presumptive, under Heir.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRESUMPTIVE HEIR. One who, if the ancestor should die immediately, would
under the present circumstances of things be his heir, but whose right of
inheritance may be defeated by the contingency of some nearer heir being
born; as a brother, who is the presumptive heir, may be defeated by the
birth of a child to the ancestor. 2 Bl. Com. 208.