The Collaborative International Dictionary of English v.0.48:

Emissary \Em"is*sa*ry\, a.
   1. Exploring; spying. --B. Jonson.
      [1913 Webster]

   2. (Anat.) Applied to the veins which pass out of the cranium
      through apertures in its walls.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Emissary \Em"is*sa*ry\, n.; pl. Emissaries. [L. emissarius,
   fr. emittere, emissum, to send out: cf. F. ['e]missaire. See
   Emit.]
   An agent employed to advance, in a covert manner, the
   interests of his employers; one sent out by any power that is
   at war with another, to create dissatisfaction among the
   people of the latter.
   [1913 Webster]

         Buzzing emissaries fill the ears
         Of listening crowds with jealousies and fears.
                                                  --Dryden.

   Syn: Emissary, Spy.

   Usage: A spy is one who enters an enemy's camp or territories
          to learn the condition of the enemy; an emissary may
          be a secret agent appointed not only to detect the
          schemes of an opposing party, but to influence their
          councils. A spy must be concealed, or he suffers
          death; an emissary may in some cases be known as the
          agent of an adversary without incurring similar
          hazard.
          [1913 Webster]

WordNet (r) 3.0 (2006):

emissary
    n 1: someone sent on a mission to represent the interests of
         someone else [syn: emissary, envoy]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "emissary":
   Hermes, Iris, Mercury, Paul Revere, Pheidippides, ambassador,
   ambassadress, apostolic delegate, attache, bearer, career diplomat,
   carrier, chancellor, charge, commercial attache, commissar,
   commissary, commissionaire, commissioner, consul, consul general,
   consular agent, courier, delegate, diplomat, diplomatic,
   diplomatic agent, diplomatic courier, diplomatist, envoy,
   envoy extraordinary, estafette, express, foreign service officer,
   go-between, herald, internuncio, legate, message-bearer, messenger,
   military attache, minister, minister plenipotentiary,
   minister resident, nuncio, plenipotentiary, post, postboy,
   postrider, resident, runner, secretary, secretary of legation,
   vice-consul, vice-legate