What does subsonic mean?
Subsonic is chiefly an adjective describing motion below the speed of sound in a particular medium. Aircraft described as subsonic cruise beneath the boundary at which the pressure disturbances produced by movement combine into the characteristic boom associated with faster flight. The term is therefore important in aeronautics, engineering, and discussions of efficiency, noise, and vehicle design. Subsonic also has an acoustic sense: it can describe vibrations or frequencies below the normal range of human hearing, overlapping with terms such as infrasonic and subaudible. The pronunciation is commonly rendered with primary stress on “son,” while the initial sub- carries secondary stress. In general writing, the word is chiefly used for its specialized technical meanings rather than as an everyday synonym for quiet or slow.
adjectiveDenoting or relating to motion below the speed of sound in a given medium. In acoustics, it may also denote sound or vibration with frequencies below the normal audible range.
- Moving or travelling below the speed of sound in the surrounding medium.
- Having a frequency below the normal audible range of human hearing.
"The aircraft was designed for efficient subsonic flight rather than high-speed supersonic travel."
"Engineers optimized the aircraft for stable, fuel-efficient subsonic cruising."
"The laboratory recorded faint subsonic vibrations through its sensitive sensors."
Subsonic marks the boundary beneath which aircraft travel without producing the characteristic boom of supersonic flight.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does subsonic come from?
Subsonic was formed in the early 20th century from sub-, meaning “below,” and sonic, a word derived from Latin sonus, “sound.” The underlying sense is therefore literally “below sound,” historically referring to motion below the speed at which sound travels. Later acoustic usage extended the idea to frequencies below the threshold of human hearing.
Related word forms
How subsonic is actually used
The word is chiefly used in technical contexts. In aeronautics it normally contrasts with supersonic, while in acoustics it is often close in meaning to infrasonic or subaudible.
Easily confused with subsonic
Subsonic describes travel below the speed of sound, whereas supersonic describes travel above it.
Both can describe frequencies below the audible range, but infrasonic more specifically emphasizes sound below approximately 20 hertz.