The Collaborative International Dictionary of English v.0.48:

Montant \Mon"tant\, n. [F.,prop., mounting, fr. monter to mount,
   fr. L. mons, montis, mountain. See Mount.]
   1. (Fencing) An upward thrust or blow. --Shak.
      [1913 Webster]

   2. (Arch.) An upright piece in any framework; a mullion or
      muntin; a stile. [R.] See Stile.
      [1913 Webster]