• 宇宙うちゅう — universe
• 宙返ちゅうがえり — somersault in the air
• 宙吊ちゅうづり — suspended in air; hanging
• 宙ちゅうに浮うく — to float in space; be unresolved

宙 combines 宀 (roof/overhead) with 由, evoking what is overhead or aloft. It extends from “hanging in midair” to broad senses like “space” and “the universe.”