Definition from Wiktionary, the free dictionary
Ancient Greek ὀκτώ (oktō, “eight”), for the eighth order of 10−3. The letter y was added, as the second term in a series running backwards through the alphabet.
- In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10−24. Symbol: y
- yoctometer / yoctometre