subsonic

1. 1.

   (of speed) less than that of sound in a designated medium

   “aircraft flying at subsonic speeds”

   Antonymssupersonicsonic

Questions about subsonic

What does subsonic mean?

subsonic means "(of speed) less than that of sound in a designated medium".

How many syllables are in subsonic?

subsonic has 3 syllables: sub-so-nic. The stress falls on "so".

What is the opposite of subsonic?

The recorded antonyms are supersonic, sonic.

Is subsonic a common word?

subsonic is banded "Rare" — specialist or archaic — most readers will not have met it. The band comes from how often the word appears in a large corpus of everyday English, not from an editor's impression.