fathometer vs sonic depth finder

fathometer and sonic depth finder both are nouns.

Word	Noun	Adjective	Verb	Adverb
fathometer	Yes	No	No	No
sonic depth finder	Yes	No	No	No

As nouns, fathometer and sonic depth finder are synonyms defined as:

fathometer and sonic depth finder: depth finder for determining depth of water or a submerged object by means of ultrasound waves

fathometer (noun)	sonic depth finder (noun)
depth finder for determining depth of water or a submerged object by means of ultrasound waves	depth finder for determining depth of water or a submerged object by means of ultrasound waves