| 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. |
| femto- pref. One quadrillionth (10-15): femtovolt. [From Danish and Norwegian femten, fifteen, from Old Norse fimmtān; see penkwe in Indo-European roots.] |
femto- pref.
One quadrillionth (10-15): femtovolt.
femto-
prefix