See giga-.

A unit of force equal to the force exerted by gravity; used to indicate the force to which a body is subjected when it is accelerated; SYN. gee.
The force of acceleration due to gravity equal to 32.1739 ft/sec2 or 386 in./sec2.
Symbol for gram.

The seventh letter of the English alphabet. It was formed by the Romans by adding a “tail” to the letter C, which represented the k sound.