Pronunciation: (tril'yun), [key]
—n., pl. -lions, (as after a numeral) -lion,
a cardinal number represented in the U.S. by 1 followed by 12 zeros, and in Great Britain by 1 followed by 18 zeros.
amounting to one trillion in number.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.