The Collaborative International Dictionary of English v.0.48:

Crossette \Cros*sette"\ (kr?s-s?t`), n. [F., dim. of crosse. See
   Crosier.] (Arch.)
   (a) A return in one of the corners of the architrave of a
       door or window; -- called also ancon, ear, elbow.
   (b) The shoulder of a joggled keystone.
       [1913 Webster]