Definition of sidereal
: of, relating to, or expressed in relation to stars or constellations : astral
sidereal was our Word of the Day on 03/30/2016. Hear the podcast!
Did You Know?
In Latin, the word for a star or constellation is sidus. Latin speakers used that word to form desiderare ("from a heavenly body") and considerare ("to think about a heavenly body"), which were adopted into English as desire and consider. Sidereal, another sidus creation, was first documented in English in 1642. Thirty-four years later, an astronomer coined the phrase "sidereal year" for the time in which the earth completes one revolution in its orbit around the sun, measured with respect to the fixed stars. Not surprisingly, other sidereal measurements of time followed, including the sidereal month, the sidereal day, the sidereal hour, and even the sidereal minute.
Origin and Etymology of sidereal
Latin sidereus, from sider-, sidus star, constellation
First Known Use: 1612
Learn More about sidereal
Seen and Heard
What made you want to look up sidereal? Please tell us where you read or heard it (including the quote, if possible).