The Collaborative International Dictionary of English v.0.48:

Janus-faced \Ja"nus-faced`\, a.
   Double-faced; deceitful.
   [1913 Webster]

   Janus-faced lock, one having duplicate faces so as to go
      upon a right or a left hand door, the key entering on
      either side indifferently. --Knight.
      [1913 Webster]