1530s, from Latin aestuarium "a tidal marsh or opening," from aestus "boiling (of the sea), tide, heat," from PIE *aidh- "to burn" (see edifice). Related: Estuaries; estuarine.
The wide lower course of a river where it flows into the sea. Estuaries experience tidal flows and their water is a changing mixture of fresh and salt.
An arm of the sea that extends inland to meet the mouth of a river.
A wide body of water formed where a large river meets the sea. It contains both fresh and salt water.