The Collaborative International Dictionary of English v.0.48:

Decrew \De*crew"\, v. i. [F. d['e]crue, n., decrease, and
   d['e]cru, p. p. of d['e]cro[^i]tre. See Decrease, and cf.
   Accrue.]
   To decrease. [Obs.] --Spenser.
   [1913 Webster]