WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. one trillionth (10^-12) of a second; one thousandth of a nanosecond
Word Usage
"The reaction event proper is a molecular drama that takes place under an exceedingly short time span - of the order of a millionth of a millionth of a second - times scientists refer to as a "picosecond"."