parsec

UK: /ˈpɑːˌsɛk/ US: (pär′sek′)

WordReference Random House Unabridged Dictionary of American English © 2026

par•sec  (pär′sek′), n. [Astron.]

1. Astronomy a unit of distance equal to that required to cause a heliocentric parallax of one second of an arc, equivalent to 206,265 times the distance from the earth to the sun, or 3.26 light-years.

• par(allax) + sec(ond)² 1910–15

Collins Concise English Dictionary © HarperCollins Publishers::

parsec / ˈpɑːˌsɛk/ noun

1. a unit of astronomical distance equal to the distance from earth at which stellar parallax would be 1 second of arc; equivalent to 3.0857 × 10¹⁶ m or 3.262 light years

Etymology: 20th Century: from parallax + second²