firth

Etymology 1

.]] Borrowed from Scots firth, furth, from Northern Middle English fyrth, from either or both Old English ford and Old Norse fjǫrðr (“firth, fjord”), from Proto-Germanic *ferþu, *ferþuz (“inlet, fjord”), from Proto-Indo-European *pértus (“crossing”), from *per- (“to carry forth”) + *-tus (suffix forming action nouns from verb roots). The English word is a doublet of fjord, ford, and port.

noun

1. An arm or inlet of the sea; a river estuary.
   The descent continues, still more steeply to Dundee (Tay Bridge), and approaching from the bridge itself this sharp descent gives the curious appearance that the station is below the level of the firth. 1947 January and February, O. S. Nock, “"The Aberdonian" in Wartime”, in Railway Magazine, page 7
   They drove on, every rise in the road lifting their sightline clear of the drystone dykes along the roadside, gifting glimpses of the firth and the islands, the blue peaks of Arran. 2022, Liam McIlvanney, The Heretic, page 440

Etymology 2

From Middle English fyrth, a metathetic variant of frith (“forest”), from Old English fyrhþe, fyrhþ (“forest, wooded country; game preserve, hunting ground”), from Proto-West Germanic *furhiþi (“forest, woodland”), Proto-Germanic *furhiþją (“forest, wooded country”), *furhiþǭ, from *furhu (“fir; pine”), from *furahō, *furhō (“fir; pine; (fir or pine) forest”), from Proto-Indo-European *pérkus (“oak”), from *perkʷ- (“oak”).

noun

1. (chiefly Northern England, Scotland) Alternative form of frith (“a forest used for hunting; a (small) wood; wooded country; land covered mainly by brushwood”)