a buoy that emits a radio signal on receiving an underwater signal from a vessel.
Origin of sonobuoy
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a buoy equipped to detect underwater noises and transmit them by radio
Word Origin for sonobuoy
from sonic + buoy
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012