Astro/æstrəʊ,æstrə,əˈstrɑː/ Definition 1 of 5Pro Tip 1/2Slang Usage Used informally, often in casual conversations about space professions. My cousin is training to become an astro. Pro Tip 2/2Not Widely Recognized Not all English speakers may understand 'astro' as 'astronomer' or 'astronaut'. I just met an astro—oh, I mean an astronomer.