a method for detecting and locating objects submerged in water by echolocation.
the apparatus used in sonar.
Also called, British, asdic.

1940–45; so(und) na(vigation) r(anging) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
sonar (ˈsəʊnɑː)
a communication and position-finding device used in underwater navigation and target detection using echolocation
[C20: from so(und) na(vigation and) r(anging)]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1946, from first letters of "sound navigation ranging," on pattern of radar.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
sonar  [%PREMIUM_LINK%]     (sō'när')  Pronunciation Key 

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  1. Short for sound navigation and ranging. A method of detecting, locating, and determining the speed of objects through the use of reflected sound waves. A sound signal is produced, and the time it takes for the signal to reach an object and for its echo to return is used to calculate the object's distance. The Doppler effect can also be used to determine the object's relative velocity. Electronic sonar systems are used for submarine navigation and for detecting schools of fish. Some mammals, especially bats, use biological sonar to navigate and detect prey in dark conditions, commonly called echolocation.

  2. The equipment or physiology used in doing this. See also Doppler effect, lidar, radar.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Abbreviations & Acronyms
sound navigation and ranging
The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
It features odd-ball technology in the form of a sonar suspension.
Compared with a conventional fish-finding sonar it is a miracle, with a
  scanning rate that runs a million times faster.
The bat uses these reflected signals for orientation and as part of its sonar
  system to detect food.
Ship traffic, seismic tests and sonar pings can make navigating the seas tricky
  for whales.
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