subsonic
sub·so·nic
adjective
1.
(of speed) less than that of sound in a designated medium
- “aircraft flying at subsonic speeds”
Origin
From sub- + sonic.
WordNet 2.1 (Princeton University). Wiktionary (CC BY-SA). WordNet 2.1 Copyright Princeton University. All rights reserved. Wiktionary content is available under the Creative Commons Attribution-ShareAlike Licence.