femto-

1.
a combining form used in the names of units of measurement which are 10− 15 (one quadrillionth) smaller than the unit denoted by the base word.
Origin
< Danish, Norwegian femt(en) fifteen + -o-
British Dictionary definitions for femto-

femto-

prefix
1.
denoting 10–15: femtometer, f
Word Origin
from Danish or Norwegian femten fifteen
femto- in Medicine

femto- pref.
One quadrillionth (10-15): femtovolt.

femto- in Technology