vice president

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An officer ranking next below a president, usually empowered to assume the president's duties under conditions such as absence, illness, or death.
• noun A deputy to a president, especially in a corporation, in charge of a specific department or location.

from The Century Dictionary.

• noun An officer who is selected in advance to fill the presidential office in case of the death, disability, or absence of the president.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A deputy to a president, often empowered to assume the position of president on his death or absence
• noun An executive in a business in charge of a department or branch

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

• noun an executive officer ranking immediately below a president; may serve in the president's place under certain circumstances