The Collaborative International Dictionary of English v.0.48:

Esprit \Es`prit"\, n. [F. See Spirit.]
   Spirit.
   [1913 Webster]

   Esprit de corps, a French phrase much used by English
      writers to denote the common spirit pervading the members
      of a body or association of persons. It implies sympathy,
      enthusiasm, devotion, and jealous regard for the honor of
      the body as a whole.
      [1913 Webster]

WordNet (r) 3.0 (2006):

esprit de corps
    n 1: the spirit of a group that makes the members want the group
         to succeed [syn: esprit de corps, morale, team
         spirit]