momentum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Physics A measure of the motion of a body equal to the product of its mass and velocity. Also called linear momentum.
2. n. Impetus of a physical object in motion.
3. n. Impetus of a nonphysical process, such as an idea or a course of events: The soaring rise in interest rates finally appeared to be losing momentum.
4. n. Philosophy An essential or constituent element; a moment.

Century Dictionary and Cyclopedia

1. n. In mech., the product of the mass and velocity of a body; the quantity of motion of a body. In all relations between bodies, such as impacts, the algebraic sum of the momenta is preserved constant. See energy.
2. n. An impulse; an impelling force; impetus.
3. n. Constituent or essential element. Compare moment, 6.
4. n. In musical notation, an eighth-rest.

Wiktionary

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

GNU Webster's 1913

1. n. (Mech.) The quantity of motion in a moving body, being always proportioned to the quantity of matter multiplied by the velocity; impetus.
2. n. Essential element, or constituent element.
3. n. 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.

WordNet 3.0

1. n. an impelling force or strength
2. n. the product of a body's mass and its velocity