The Collaborative International Dictionary of English v.0.48:

Subreption \Sub*rep"tion\, n. [L. subreptio, fr. subripere,
   subreptum, to snatch or take away secretly: cf. F.
   subreption. See Surreptitious.]
   The act of obtaining a favor by surprise, or by unfair
   representation through suppression or fraudulent concealment
   of facts. --Bp. Hall.
   [1913 Webster]

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

SUBREPTION, French law. By this word is understood the fraud committed to
obtain a pardon, title, or grant, by alleging facts contrary to truth.