Firth
/fɜːrθ/
Definition 1 of 1
Pro Tip 1/3Geographical Term
Firth is often used to name specific geographic locations in Scotland and occasionally in other parts of the United Kingdom. 
Let's visit the Firth of Forth when we go to Scotland.
Pro Tip 2/3Not a River
Firth refers to a sea inlet or estuary, not the river itself, but it may be part of a river's tidal mouth region. 
The salmon were caught in the firth, not far from where the river meets the sea.
Pro Tip 3/3Natural Landmarks
A firth can serve as a natural landmark and is commonly used as such in directions or descriptions of a location. 
You'll see the ancient castle overlooking the firth.