Search Result for "subsonic": 
Wordnet 3.0

ADJECTIVE (1)

1. (of speed) less than that of sound in a designated medium;
- Example: "aircraft flying at subsonic speeds"



WordNet (r) 3.0 (2006):

subsonic
    adj 1: (of speed) less than that of sound in a designated
           medium; "aircraft flying at subsonic speeds" [ant:
           sonic, supersonic, transonic]