subsonic

American  

[suhb-son-ik] / sʌbˈsɒn ɪk /

adjective

1. noting or pertaining to a speed less than that of sound in air at the same height above sea level.

2. infrasonic.

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subsonic British  

/ sʌbˈsɒnɪk /

adjective

1. being, having, or travelling at a velocity below that of sound

   a subsonic aircraft

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subsonic Scientific  

/ sŭb-sŏn′ĭk /

1. Having a speed less than that of sound in a designated medium, usually air; having a velocity less than Mach 1.

2. Compare hypersonic supersonic transonic

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Other Word Forms

• subsonically adverb

Etymology

Origin of subsonic

1940–45; sub- + sonic ( def. )

Compare meaning

How does subsonic compare to similar and commonly confused words? Explore the most common comparisons:

• subsonic vs. supersonic

Example Sentences

Even then Tomahawks, which fly at subsonic speeds at a low altitude, could be vulnerable to Russian air defenses.

From The Wall Street Journal • Oct. 16, 2025

Right above the shores of Huntington Beach, a retired American subsonic T-33 fighter jet darted across the blue canvas of a clear afternoon sky, leaving a spiraling plume of smoke in its wake.

From Los Angeles Times • Oct. 4, 2025

In terms of purely destructive power, however, hypersonic missiles are not hugely different from supersonic or subsonic cruise missiles, according to Mr Freer.

From BBC • Aug. 21, 2025

Nuclear forces also are being modernized with $37.7 billion on new forces, and $11 billion for a mix of both hypersonic and long-range subsonic weapons that can strike from land, air and sea.

From Washington Times • May 17, 2023

The horse didn’t seem happy about it, but he slowed to subsonic as they zipped through the city streets.

From "The Son of Neptune" by Rick Riordan