Estuary
Etymology
From Latin "aestuarium" ("tidal marsh, channel"), from "aestus" ("tide, surge, boiling heat"). The root ties the tide’s rhythmic swelling to the idea of boiling or seething.
noun · /ES-choo-air-ee/
The tidal mouth of a river, where fresh water meets and mixes with the salt water of the sea.
What it names
A specific, ecologically rich zone — the brackish transition between river and ocean — often confused with a delta.
Example
Salmon paused in the estuary before pushing upriver to spawn.
Related idea
An estuary is a funnel where the sea reaches inland; a delta is a fan of sediment the river builds out into the sea.