Dictionary.net

• A unit for the measurement of many small lengths, such that 1010 of these units make one meter; the ten millionth part of a millimeter.

2010 - New Age Dictionary Database
By Oddity Software

• A unit for the measurement of many small lengths, such that 1010 of these units make one meter; the ten millionth part of a millimeter.

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.