bathometer

from WordNet (r) 3.0 (2006)

bathometer
    n 1: an instrument that measures the depth of water [syn:
         {bathymeter}, {bathometer}]

from The Collaborative International Dictionary of English v.0.48

Bathometer \Ba*thom"e*ter\, n. [Gr. baqo`s depth + -meter.]
   An instrument for measuring depths, esp. one for taking
   soundings without a sounding line.
   [1913 Webster]