1670s, from Latin quintus "the fifth" (see quinque-) + ending from million. Cf. billion. In Great Britain, the fifth power of a million (1 followed by 30 zeroes); in U.S. the sixth power of a thousand (1 followed by 18 zeroes).
10^30 in Europe (this is called a nonillion in the United States and Canada). 10^18 in the United States and Canada (this is called a trillion in Europe). [Collins dictionary].