What does "astro-" mean in Greek?

In Greek, the prefix "astro-" translates to 'star'. This prefix is commonly found in words related to astronomy, astrology, and other fields that involve the study or reference to celestial bodies. The root comes from the ancient Greek word "ἀστήρ" (astēr), which means "star". This is why it is used in various terms that have a direct connection to stars and celestial phenomena.

The other options represent different meanings and roots in Greek. "Self" corresponds more closely to the prefix "auto-", "under" relates to "hypo-", while the option indicating "both" does not accurately apply since "astro-" has a singular meaning. Thus, the correct focus on the definition of "astro-" confirming it means 'star' solidifies the reasoning for selecting that answer.