Lagoon and Tarn

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

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

Tarn noun - A mountain lake (especially one formed by glaciers).

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