Source : Webster's Revised Unabridged Dictionary (1913)

Reconnoissance \Re*con"nois*sance\, Reconnaissance
\Re*con"nais*sance\ (r?-k?n"n?s-s?ns), n. [F. See
   {Recognizance}.]
   The act of reconnoitering; preliminary examination or survey.
   Specifically:
   (a) (Geol.) An examination or survey of a region in reference
       to its general geological character.
   (b) (Engin.) An examination of a region as to its general
       natural features, preparatory to a more particular survey
       for the purposes of triangulation, or of determining the
       location of a public work.
   (c) (Mil.) An examination of a territory, or of an enemy's
       position, for the purpose of obtaining information
       necessary for directing military operations; a
       preparatory expedition.

   {Reconnoissance in force} (Mil.), a demonstration or attack
      by a large force of troops for the purpose of discovering
      the position and strength of an enemy.