Firth is a word in the English and Scots languages used to denote various coastal waters in the United Kingdom, predominantly within Scotland. In the Northern Isles, it more often refers to a smaller inlet.

The Economist, 4 Dec. 2019 Gray and harbor seals are a common sight in this firth, or estuary, where several major rivers meet the North Sea. National Geographic, 16 Feb. 2017

They continued their course until they came to a place where a firth penetrated far into the country.

Definition of firth noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

firth (fɜːθ) or frith n (Physical Geography) a relatively narrow inlet of the sea, esp in Scotland [C15: from Old Norse fjörthr fiord]

Jun 24, 2025 · Noun firth (plural firths) An arm or inlet of the sea; a river estuary. [from c. 1600]

May 16, 2018 · The firth is named after Scotland’s largest river, River Tay, that discharges its waters into the Firth of Tay. Other firths found in Scotland include the Dornoch Firth, the Firth of Forth, the Firth …