sonar vs echo sounder

sonar and echo sounder both are nouns.

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

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

sonar and echo sounder: 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 sonar include asdic.

sonar (noun)	echo sounder (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