(n)a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return, Syn.asdic, echo sounder
The Collaborative International Dictionary of English (GCIDE) v.0.53Collaborative International Dictionary (GCIDE)
n. One who, or that which; sounds; specifically, an instrument used in telegraphy in place of a register, the communications being read by sound. [ 1913 Webster ]