Loch
Loch (), is the Irish and Scottish Gaelic word for a lake and a sea inlet. It is cognate with the Manx lough, Cornish logh, and the Welsh word for lake, llwch.
In English and Hiberno-English, the anglicised spelling lough is commonly found in place names, pronounced the same way as loch. In Scottish English, 'loch' is always used.
Some lochs could also be called firths, fjords, estuaries, straits or bays. Sea-inlet lochs are often called sea lochs or sea loughs
Background
This name for a body of water is Insular Celtic
in origin and is applied to most lakes in
Scotland and to many sea inlets in the west and north of Scotland. The word is Indo-European in origin; cf. Latin lacus.
Lowland Scots orthography, like Scottish Gaelic, Welsh and Irish, represents /x/ with ch, so the word was borrowed with identical spelling.
English borrowed the word separately from a number of loughs in the previous Cumbric language areas of Northumbria and Cumbria. Earlier forms of English included the sound /x/ as ch (compare Scots bricht with English bright). However, by the time Scotland and England joined under a single parliament, English had lost the /x/ sound. This form was therefore used when the English settled Ireland. The Scots convention of using CH remained, hence the modern Scottish English loch.
