estuary

What it means

1. A coastal water body where ocean tides and river water merge, resulting in a brackish water zone.

   The railway then follows the widening estuary of the river, which at high tide has the appearance of a lake, but at low water presents a rather cheerless expanse of dark mud.

   1953 February, H. A. Vallance, “To Brighton through the Shoreham Gap”, in Railway Magazine, page 82

   1 more example

   There's something special about tidal estuaries, due to the abundance of wildlife and the ever-changing scenes as the water ebbs or rises. Throw in some moody skies and filtered sunlight, and the views can resemble a painting by Turner - only you don't have to go to the National Gallery to see this, it's brought to your seat on a train.

   2020 December 2, Paul Bigland, “My weirdest and wackiest Rover yet”, in Rail, page 65

2. An ocean inlet also fed by fresh river water.

In a sentence

The railway then follows the widening estuary of the river, which at high tide has the appearance of a lake, but at low water presents a rather cheerless expanse of dark mud.

1953 February, H. A. Vallance, “To Brighton through the Shoreham Gap”, in Railway Magazine, page 82

Where it comes from

1. Latinaestuarium“creek”, “estuary of a river”
2. Englishestuary

From Latin aestuarium (“creek”, “estuary of a river”).