charge d'affaires

from The Century Dictionary.

• One who transacts diplomatic business at a foreign court during the absence of his superior, the ambassador or minister.
• An envoy to a state to which a diplomatist of a higher grade is not sent.
• noun An officer or other person left in charge of any business or office during the temporary absence of the chief.

from the GNU version of the Collaborative International Dictionary of English.

• noun A diplomatic representative, or minister of an inferior grade, accredited by the government of one state to the minister of foreign affairs of another; also, a substitute, ad interim, for an ambassador or minister plenipotentiary.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the official temporarily in charge of a diplomatic mission in the absence of the ambassador