The Collaborative International Dictionary of English v.0.48:

Precative \Prec"a*tive\, Precatory \Prec"a*to*ry\, a. [L.
   precativus, precatorius, fr. precari to pray. See
   Precarious.]
   Suppliant; beseeching. --Bp. Hopkins.
   [1913 Webster]

   Precatory words (Law), words of recommendation, request,
      entreaty, wish, or expectation, employed in wills, as
      distinguished from express directions; -- in some cases
      creating a trust. --Jarman.
      [1913 Webster]