Source : Webster's Revised Unabridged Dictionary (1913)

Sortie \Sor"tie\ (?; 277), n. [F., fr. sortir to go out, to
   issue, probably fr. L. sortus, for surrectus, p. p. of
   surgere to raise up, to rise up. See {Source}.] (Mil.)
   The sudden issuing of a body of troops, usually small, from a
   besieged place to attack or harass the besiegers; a sally.

Source : WordNet®

sortie
     n 1: a military action in which besieged troops burst forth from
          their position [syn: {sally}]
     2: (military) an operational flight by a single aircraft (as in
        a military operation)