Webster's Revised Unabridged Dictionary · 1913

(Metric System, Electricity, Mechanics, etc.) Combining forms signifying: (a) Great, extended, powerful; as, megascope, megacosm.

(Metric System, Electricity, Mechanics, etc.) A million times, a million of; as, megabyte, a million bytes; megawatt, a million watts; megameter, a million meters; megafarad, a million farads; megohm, a million ohms.