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.

Source: Webster's Revised Unabridged Dictionary (1913)