Noun

1. the product of its mass and velocity.
2. The impetus, either of a body in motion, or of an idea or course of events. (i.e: a moment)
   • 1843, Nathaniel Hawthorne, "The Old Apple Dealer", in Mosses from an Old Manse

     The travellers swarm forth from the cars. All are full of the momentum which they have caught from their mode of conveyance.

   • 1882, Thomas Hardy, Two on a Tower

     Their intention to become husband and wife, at first halting and timorous, had accumulated momentum with the lapse of hours, till it now bore down every obstacle in its course.