The Collaborative International Dictionary of English v.0.48:

Legate \Leg"ate\ (l[e^]g"[asl]t), n. [OE. legat, L. legatus, fr.
   legare to send with a commission or charge, to depute, fr.
   lex, legis, law: cf. F. l['e]gat, It. legato. See Legal.]
   1. An ambassador or envoy.
      [1913 Webster]

   2. An ecclesiastic representing the pope and invested with
      the authority of the Holy See.
      [1913 Webster]

   Note: Legates are of three kinds: (a) Legates a latere, now
         always cardinals. They are called ordinary or
         extraordinary legates, the former governing provinces,
         and the latter class being sent to foreign countries on
         extraordinary occasions. (b) Legati missi, who
         correspond to the ambassadors of temporal governments.
         (c) Legati nati, or legates by virtue of their
         office, as the archbishops of Salzburg and Prague.
         [1913 Webster]

   3. (Rom. Hist.)
      (a) An official assistant given to a general or to the
          governor of a province.
      (b) Under the emperors, a governor sent to a province.
          [1913 Webster]

WordNet (r) 3.0 (2006):

legate
    n 1: a member of a legation [syn: legate, official emissary]