echo sounder vs sonar

echo sounder and sonar both are nouns.

Word	Noun	Adjective	Verb	Adverb
echo sounder	Yes	No	No	No
sonar	Yes	No	No	No

As nouns, echo sounder and sonar are synonyms defined as:

echo sounder and sonar: a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return

Other synonyms of echo sounder include asdic.

echo sounder (noun)	sonar (noun)
a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return	a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return