megabyte: 1 million bytes, referring to a unit of data or computer memory

A byte consists of eight bits, a bit being the basic unit of information on computers. (Bit is a shortening of binary digit.) The term megabit, in use since the 1950s, was followed shortly by megabyte. However, the first mega- word to be familiar to most Americans was probably megaton -- a unit for measuring the explosive force of atomic bombs -- first recorded in the early fifties. A megaton is equal to one million tons of TNT. Since the 1950s a number of mega- terms have entered everyday speech. These include megabucks, megadose, megavitamin, megamillionaire, and megarich.

Mega- itself goes back to Indo-European *meg-, meaning 'great' and comes to English from Greek. The Germanic form of the root gave us much, while the Latin form resulted in magnificent, magnitude, master, and majority, among other words.