The Collaborative International Dictionary of English v.0.48:

Decrescent \De*cres"cent\, a. [L. decrescens, p. pr. of
   decrescere. See Decrease.]
   Becoming less by gradual diminution; decreasing; as, a
   decrescent moon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decrescent \De*cres"cent\, n. (Her.)
   A crescent with the horns directed towards the sinister.
   --Cussans.
   [1913 Webster]