Lough

Loch (/ˈlɒx/) is the Irish, Scottish Gaelic and Scots word for a lake or for a sea inlet. It is cognate with the Manx lough, Cornish logh, and the Welsh word for lake, llyn.

In English English and Hiberno-English, the anglicised spelling lough is commonly found in place names, pronounced the same way as loch; in Lowland Scots and Scottish English, the spelling "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.

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.

...
Wikipedia