(Greek: large, great, big, powerful)
When measuring in the metric [decimal] system, it means a million [U.S.] or millionfold [U.K.]: 106 [1 000 000]. The metric symbol for mega- is M.
A dose of a vitamin, or vitamins, vastly exceeding the amount recommended, or required, for nutritional balance.
A unit of electricity equivalent to one million volts.
In radiation therapy, voltage greater than one megavolt.