astro-

American Heritage® Dictionary of the English Language, Fourth Edition

1. Star: astrophysics.
2. Celestial body: astrometry.
3. Outer space: astronaut.
4. The aster of a cell: astrosphere.

Century Dictionary and Cyclopedia

1. n. The initial element in many compound scientific terms of Greek origin, meaning star.

Wiktionary

1. pertaining to celestial bodies: fixed stars, wandering stars (planets), etc.

GNU Webster's 1913

1. The combining form of Greek word 'a`stron, meaning star.