Envoy

Webster's Dictionary

(1): ( n.) One dispatched upon an errand or mission; a messenger; esp., a person deputed by a sovereign or a government to negotiate a treaty, or transact other business, with a foreign sovereign or government; a minister accredited to a foreign government. An envoy's rank is below that of an ambassador.

(2): ( n.) An explanatory or commendatory postscript to a poem, essay, or book; - also in the French from, l'envoi.