Depth finder and Sonar

Depth finder noun - Navigational instrument used to measure the depth of a body of water (as by ultrasound or radar).

Sonar and depth finder are semantically related. In some cases you can use "Sonar" instead a noun phrase "Depth finder".

Sonar noun - 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.

Depth finder and sonar are semantically related. You can use "Depth finder" instead a noun "Sonar".