Yottasecond 

The largest multiple of a second that is measurable. It's about 10000000000000000000000000 seconds.

Yottasecond is the largest multiple second measurable. It's symbol is yt.

Yottasecond by Clawbo December 16, 2008

yoctosecond

The smallest MEASURABLE time unit known today, 1x10^(-24) seconds. Obviously, smaller units of time exist, but proper equipment and methodology for measuring them does not yet exist. Light travels 2.9979x10^(-16) meters in one yoctosecond, not the 3.33km stated above.

Learn to multiply. This isn't even an 'urban' word, so why is it defined here?

yoctosecond by iNsAniTy August 30, 2005

yoctosecond

The smallest unit of time known today. It is on septillionth of a second, or about 0,000000000000000000000001 second(10^-24).

Light can travel a distance of approximately 3.33 kilometers in one yoctosecond.

yoctosecond by Tom Something August 4, 2005