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.

Nearby words

  1. astride,
  2. astringe,
  3. astringent,
  4. astringer,
  5. astrionics,
  6. astro-inertial guidance,
  7. astroarchaeology,
  8. astrobiology,
  9. astroblast,
  10. astroblastoma

Compare cosmo-.

Origin of astro-

< Greek, combining form of ástron a star, constellation, akin to astḗr star; cf. aster, -aster2 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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

Word Origin and History for astro-


element active in English word formation from mid-18c. and meaning "star or celestial body; outer space," from Greek astro-, stem and comb. form of astron "star," related to aster "star" (see star (n.)). In ancient Greek, aster typically was "a star" and astron mostly in plural, "the stars." In singular it mostly meant "Sirius" (the brightest star).

Online Etymology Dictionary, © 2010 Douglas Harper

Science 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.