Standard Lemma guide

femtosecond

noun · 2 senses · updated from the 2026-07-25 local source snapshot

Definitions and examples are grouped by meaning. Pronunciation, history, word forms, translations, descendants, synonyms, antonyms, derived terms, and related words appear whenever the source provides them.

Sound

Pronunciation

Each Play button uses your device's default local English voice, or a natural local fallback. The selected voice name appears after playback. This is synthesized speech, not a source recording.

No pronunciation record was provided for this word.

1

noun

Meaning 1

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

Definition source: English Wiktionary via Wiktextract

Topics: metrology

Examples

  • Holonyms: picosecond < nanosecond < microsecond < millisecond < centisecond < decisecond < second < decasecond < minute < hectosecond < kilosecond < hour < day < week < megasecond < fortnight < month < year < gigasecond < century < kiloannum, kiloyear, millennium < terasecond < mega-annum, megayear < petasecond < giga-annum, gigayear < exasecond < zettasecond < yottasecond < ronnasecond < quettasecond
  • Meronyms: quectosecond < rontosecond < yoctosecond < zeptosecond < attosecond

Meaning relationships

Synonyms: none provided

Antonyms: none provided

2

noun

Meaning 2

one quadrillionth (10^-15) of a second; one thousandth of a picosecond

Definition source: Princeton WordNet 3.0

No example sentence was provided for this meaning.

Meaning relationships

Synonyms: none provided

Antonyms: none provided

Broader terms: time unit, unit of time

History

Etymology

Etymology tree Proto-Indo-European *pénkwe Proto-Germanic *fimf Proto-Indo-European *déḱm̥ Proto-Germanic *tehun Proto-Germanic *fimftehun Old Norse fimmtánder. Danish femtender. English femto- English second English femtosecond From femto- + second.

Across languages

Translations

9 source translations are retained for this English entry.

  • Chinese Mandarin: 飛秒 /飞秒 (fēimiǎo) — unit of time, equal to 10−15 second
  • Chinese Mandarin: 毫微微秒 (háowēiwēimiǎo) — unit of time, equal to 10−15 second
  • Czech: femtosekunda — unit of time, equal to 10−15 second
  • Dutch: femtoseconde — unit of time, equal to 10−15 second
  • French: femtoseconde — unit of time, equal to 10−15 second
  • Hungarian: femtoszekundum — unit of time, equal to 10−15 second
  • Spanish: femtosegundo — unit of time, equal to 10−15 second
  • Swedish: femtosekund — unit of time, equal to 10−15 second
  • Ukrainian: фемтосекундний (femtosekundnyj) — unit of time, equal to 10−15 second