echo sounder vs sub

echo sounder and sub both are nouns.

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

echo sounder (noun)	sub (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 submersible warship usually armed with torpedoes
	a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States

echo sounder (verb)	sub (verb)
	be a substitute