From Longman Dictionary of Contemporary Englishfirthfirth /fɜːθ $ fɜːrθ/ noun [countable] DNSGa narrow area of sea between two areas of land, or the place where a river flows into the sea – used especially in Scotland the Firth of Forth
Examples from the Corpus
firth• Control of Belhaven Brewery first went firth of the forth when Nasmu Virani bought it in 1984. 