Astro is a prefix that refers to celestial objects such as stars, planets, and galaxies. It is derived from the Greek word "astron," which means star. Some synonyms for the term "astro" include celestial, stellar, astronomic, and galactic. These words convey the same meaning as "astro," describing space and outer space-related topics. For example, one might say "astrology" as a synonym for the study of the stars and planets' influence on human affairs. "Astrophysics" is another synonym that refers to the scientific study of the physical properties and behaviors of the celestial bodies. Overall, these synonyms help expand our vocabulary when referring to space-related concepts.