The Collaborative International Dictionary of English v.0.48:

Diplomacy \Di*plo"ma*cy\, n. [F. diplomatie. This word, like
   supremacy, retains the accent of its original. See
   Diploma.]
   1. The art and practice of conducting negotiations between
      nations (particularly in securing treaties), including the
      methods and forms usually employed.
      [1913 Webster]

   2. Dexterity or skill in securing advantages; tact.
      [1913 Webster]

   3. The body of ministers or envoys resident at a court; the
      diplomatic body. [R.] --Burke. Diplomat

WordNet (r) 3.0 (2006):

diplomacy
    n 1: negotiation between nations [syn: diplomacy, diplomatic
         negotiations]
    2: subtly skillful handling of a situation [syn: delicacy,
       diplomacy, discreetness, finesse]
    3: wisdom in the management of public affairs [syn:
       statesmanship, statecraft, diplomacy]

The Devil's Dictionary (1881-1906):

DIPLOMACY, n.  The patriotic art of lying for one's country.