(1) Having to do with sound. (2) Having to do with the speed of sound in air (about 750 miles per hour).
Example:
With a sonic depth finder, they determined the depth of the lake by bouncing a sound signal off the bottom.
In 1947 a plane burst the sound barrier and created a sonic boom for the first time. Now even commercial jetliners, including the Concorde, leave sonic booms in their wake as they exceed the speed of sound.