duration

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

• noun Continuance or persistence in time.
• noun A period of existence or persistence.
• noun The number of years required to receive the present value of future payments, both of interest and principle, of a bond, often used as an indicator of a bond's price volatility resulting from changes in interest rates.

from The Century Dictionary.

• noun Continuance in time; also, the length of time during which anything continues: as, the duration of life or of a partnership; the duration of a tone or note in music; the duration of an eclipse.

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

• noun The state or quality of lasting; continuance in time; the portion of time during which anything exists.

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

• noun An amount of time or a particular time interval
• noun The time taken for the current situation to end, especially the current war
• noun finance A measure of the sensitivity of the price of a financial asset to changes in interest rates, computed for a simple bond as a weighted average of the maturities of the interest and principal payments associated with it.

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

• noun continuance in time
• noun the period of time during which something continues
• noun the property of enduring or continuing in time