Source : Webster's Revised Unabridged Dictionary (1913)

Tirailleur \Ti`rail`leur"\, n. [F., from tirailler to skirmish,
   wrest, from tirer to draw.] (Mil.)
   Formerly, a member of an independent body of marksmen in the
   French army. They were used sometimes in front of the army to
   annoy the enemy, sometimes in the rear to check his pursuit.
   The term is now applied to all troops acting as skirmishers.