The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "sortie":
   aggravated assault, aggression, air cover, air raid, air support,
   amphibious attack, armed assault, assailing, assailment, assault,
   attack, banzai attack, blitz, blitzkrieg, bombing, breakthrough,
   charge, counterattack, counteroffensive, coup de main, cover,
   crippling attack, dead set at, descent on, diversion,
   diversionary attack, drive, dry run, flank attack, frontal attack,
   gas attack, head-on attack, infiltration, lightning attack,
   lightning war, mass attack, megadeath, milk run, mission, mugging,
   offense, offensive, onset, onslaught, overkill, panzer warfare,
   push, reconnaissance, reconnaissance mission, run against, run at,
   rush, sally, scramble, shock tactics, shuttle raid, strafing,
   strike, training mission, umbrella, unprovoked assault