from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A buoy equipped with an acoustic receiver and a radio transmitter that emits radio signals when it detects underwater sounds.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A buoy that sends a radio signal when it detects the sound of underwater objects (such as submarines)
From sonar + buoy (Wiktionary)