# femtosecond

> English word · Noun · frequency rank #84,242

## Definitions
1. An SI unit of time equal to 10⁻¹⁵ seconds. Symbol: fs

## Etymology
From femto- + second.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-09-03.
Canonical page: https://plainspell.com/en/word/femtosecond