noun, noun which may take the genitive case particle 'no'
subsonic speed
Technical term used in physics and engineering to describe speeds below the speed of sound. Often used attributively with の.
This aircraft cruises at subsonic speed.
Analyze subsonic flow.
亜音速 refers to speeds below the speed of sound, the direct opposite of 超音速's speeds above it.
Compound of 亜 (a, 'sub-') + 音速 (onsoku, 'speed of sound'). A modern technical coinage.