Lagoon and Millpond

Lagoon noun - A body of water cut off from a larger body by a reef of sand or coral.

Millpond and lagoon are semantically related In some cases you can use "Millpond" instead a noun "Lagoon".

Millpond noun - A pond formed by damming a stream to provide a head of water to turn a mill wheel.

Lagoon and millpond are semantically related in collection of liquid topic. You can use "Lagoon" instead a noun "Millpond", if it concerns topics such as small body of water, inland body of water.