The Collaborative International Dictionary of English v.0.48:

Allonge \Al*longe"\, n. [F. allonge, earlier alonge, a
   lengthening. See Allonge, v., and cf. Lunge.]
   1. (Fencing) A thrust or pass; a lunge.
      [1913 Webster]

   2. A slip of paper attached to a bill of exchange for
      receiving indorsements, when the back of the bill itself
      is already full; a rider. [A French usage] --Abbott.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Allonge \Al*longe"\, v. i. [F. allonger; [`a] (L. ad) + long (L.
   longus) long.]
   To thrust with a sword; to lunge.
   [1913 Webster]