The term "echo sounder" refers to a device that uses sonar technology to measure the depth of water. There are several other terms for this device that can be used interchangeably. One of the most commonly used synonyms is "sonar", which refers to any device that uses sound waves to detect objects in its vicinity. Other synonyms include "depth sounder", "fish finder", and "sonic depth finder". These terms all refer to the same type of device and are often used by marine biologists, fishermen, and sailors to navigate waters safely. Regardless of the term used, all echo sounders serve a similar and important purpose in marine exploration and navigation.