bathometern.

/bəˈθɒmɪtə/Etymology: < Greek βάθος depth + -meter comb. form2.
1875 J. Prestwich in (Royal Soc.) 165 616 Obtained, by means of his bathometer..the low readings given.
This entry has not yet been fully updated (first published 1885; most recently modified version published online March 2018).