momentum

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

• noun Physics A quantity used to measure the motion of a body, equal to the product of the body's mass and its velocity.
• noun The force or energy exhibited by a moving body.
• noun The driving force or advancing strength of a development or course of events.
• noun Philosophy An essential or constituent element; a moment.

from The Century Dictionary.

• noun In mech., the product of the mass and velocity of a body; the quantity of motion of a body.
• noun An impulse; an impelling force; impetus.
• noun Constituent or essential element. Compare moment, 6.
• noun In musical notation, an eighth-rest.

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

• noun (Mech.) The quantity of motion in a moving body, being always proportioned to the quantity of matter multiplied by the velocity; impetus.
• noun Essential element, or constituent element.
• noun A property of an activity or course of events, viewed as analogous to forward motion or to physical momentum (def. 1), such that the activity is believed to be able to continue moving forward without further application of force or effort; -- often used to describe an increase in the acquisition of public support for a purpose.

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

• noun physics (of a body in motion) the product of its mass and velocity.
• noun The impetus, either of a body in motion, or of an idea or course of events. (i.e: a moment)

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

• noun an impelling force or strength
• noun the product of a body's mass and its velocity