Really, very, uber-, super-.
Very large, great.
In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by one million (10⁶.) SI Symbol: M.
Multiplying the unit to which it is attached by 2¹³ × 5³ (= 1,024,000, the binary round number closest to a million).
Multiplying the unit to which it is attached by 2²⁰ (= 1,048,576, the binary number closest to a million). Computing symbol: Mi.
A syncopic variant of super-.