Momentum \Mo*men"tum\, n.; pl. L. {Momenta}, F. {Momentums}. [L. See {Moment}.] 1. (Mech.) The quantity of motion in a moving body, being always proportioned to the quantity of matter multiplied into the velocity; impetus. 2. Essential element, or constituent element. I shall state the several momenta of the distinction in separate propositions. --Sir W. Hamilton.