Source : Webster's Revised Unabridged Dictionary (1913)

Janus \Ja"nus\, n. [L. See {January}.] (Rom. Antiq.)
   A Latin deity represented with two faces looking in opposite
   directions. Numa is said to have dedicated to Janus the
   covered passage at Rome, near the Forum, which is usually
   called the Temple of Janus. This passage was open in war and
   closed in peace. --Dr. W. Smith.

   {Janus cloth}, a fabric having both sides dressed, the sides
      being of different colors, -- used for reversible
      garments.

Source : WordNet®

Janus
     n : (Roman mythology) the Roman god of doorways and passages; is
         depicted with two faces on opposite sides of his head

Source : Free On-Line Dictionary of Computing

Janus
     
        1. Distributed language with an ask/tell constraint system.
     
        {qdjanus} is a Janus-to-{Prolog} compiler for {Sicstus Prolog}
        and {jc} is compiles to {C}.
     
        ["Janus: A Step Towards Distributed Constraint Programming",
        V. Saraswat  et al in Logic
        Programming: Proc 1990 North Am Conf, S. Debray et al eds, MIT
        Press 1990].
     
        ["Programming in Janus", Saraswat, Kahn, and Levy].
     
        2. W.M. Waite, U Colorado.  Intermediate language, claimed as
        an implementation of {UNCOL}.  Used on {CDC 6600}.
     
        ["Experience with the Universal Intermediate Language Janus",
        B.K. Haddon et al, Soft Prac & Exp 8(5):601- 616 (Sep 1978)].