Save This Word!

a combining form with the meaning “pertaining to stars or celestial bodies, or to activities, as spaceflight, taking place outside the earth's atmosphere,” used in the formation of compound words: astronautics; astrophotography.
There are grammar debates that never die; and the ones highlighted in the questions in this quiz are sure to rile everyone up once again. Do you know how to answer the questions that cause some of the greatest grammar debates?
Question 1 of 7
Which sentence is correct?
Compare cosmo-.

Origin of astro-

<Greek, combining form of ástron a star, constellation, akin to astḗrstar; cf. aster, -aster2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does astro- mean?

Astro- is a combining form used like a prefix meaning “related to stars, celestial bodies, and outer space.” It is often used in scientific terms, especially in—you guessed it—astronomy.

Astro– is also sometimes used to refer to something that is star-shaped, as in an astrocyte, a type of star-shaped cell in the brain and spinal cord.

Astro- comes from the Greek ástron, meaning “star.” The Greek ástron is also related to such words as asteroid and even the star itself. The word astronomy comes from a Greek word that literally (and poetically) means “star-arranging.”

What are variants of astro-?

When combined with words or word elements that begin with a vowel, astro- becomes astr-.

Examples of astro-

You have likely heard of the word (and even dreamed of becoming an) astronaut.

As we know, astro- means “star.” How about -naut? It ultimately comes from the Greek naútēs, meaning “sailor.” Astronaut literally—and again, so poetically— translates to “star sailor.”

What are some other words that use the combining form astro-?

Learn about some other applications of astro- in our Vocab Builder article on Astroturf.

Similar to astro- are the combining forms cosmo- and cosm- (think cosmos). Learn more about these forms in our Words That Use cosmo- and Words That Use cosm- articles.

Break it down!

If navigating refers to moving ships in the water or planes in the sky, then what is astrogating?

How to use astro- in a sentence

British Dictionary definitions for astro-


combining form
indicating a heavenly body, star, or star-shaped structureastrology; astrocyte
indicating outer spaceastronautics

Word Origin for astro-

from Greek, from astron star
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for astro-


A prefix that means “star” (as in astrophysics), “celestial body” (as in astronomy), or “outer space” (as in astronaut).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.