—n. 1. quantity or amount: the least quantum of evidence. 2. a particular amount.
3. a share or portion.
4. a large quantity; bulk.
5. Physics. a. the smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation.
b. the fundamental unit of a quantized physical magnitude, as angular momentum.
—adj. sudden and significant: a quantum increase in productivity.