bathometer vs bathymeter

bathometer and bathymeter both are nouns.

Word	Noun	Adjective	Verb	Adverb
bathometer	Yes	No	No	No
bathymeter	Yes	No	No	No

As nouns, bathometer and bathymeter are synonyms defined as:

bathometer and bathymeter: an instrument that measures the depth of water

bathometer (noun)	bathymeter (noun)
an instrument that measures the depth of water	an instrument that measures the depth of water