The Collaborative International Dictionary of English v.0.48:

Preengage \Pre`["e]n*gage"\, v. t. [imp. & p. p.
   Pre["e]ngaged; p. pr. & vb. n. Pre["e]ngaging.]
   To engage by previous contract; to bind or attach previously;
   to preoccupy.
   [1913 Webster]

         But he was pre["e]ngaged by former ties. --Dryden.
   [1913 Webster]