Firth

A firth is a term in English and Scots used for various coastal waters in the United Kingdom, mostly in Scotland, generally referring to a broad estuary; it is linguistically related to the Scandinavian words fjord and fjard, both descending from a Proto-Germanic root meaning sailable waterway. Firths are more common on Scotland's east coast and in the southwest, with the Firth of Clyde as a western exception, while the similar inlets of the west Highland coast are usually called sea lochs instead. A firth typically forms from ice age glaciation acting on a river valley, with tidal seawater pushing upriver and eroding the riverbed wider into the estuary seen today.