fathometer vs depth finder

fathometer and depth finder both are nouns.

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

As nouns, depth finder is a hypernym of fathometer; that is, depth finder is a word with a broader meaning than fathometer:

fathometer: depth finder for determining depth of water or a submerged object by means of ultrasound waves
depth finder: navigational instrument used to measure the depth of a body of water (as by ultrasound or radar)

fathometer (noun)	depth finder (noun)
depth finder for determining depth of water or a submerged object by means of ultrasound waves	navigational instrument used to measure the depth of a body of water (as by ultrasound or radar)