emissary

noun

Etymology: From French émissaire, from Latin emissarius (“agent, scout, spy”).

1. An agent sent on a mission to represent the interests of someone else.

   “The small group around Ch’en Tu-hsiu that had remained at headquarters hastily sent an emissary—Chang Kuo-t’ao—to Nanch’ang. Though Chang set out immediately, he did not reach Nanch’ang until July 31, the day before the rising.”

2. An agent sent on a mission to represent the interests of someone else.

   “Near-synonym: missionary”

3. A venous channel in the skull.
4. An underground channel by which the water of a lake escapes.