Loch is the Scots word for 'lake', including those inlets of the sea more fully called 'sea lochs such as Loch Fyne, Holy Loch, Loch Long,and Loch Awe. Fresh-water lochs include Loch Lomond, Loch Ness and Loch Earn. The word is the Gaelic form of a common Indo-European root which also gives 'lake' in current English and llwch in Welsh, as well as locus in Latin.
- It is sometimes said that the Lake of Menteith is the only lake in Scotland (the other bodies of water being lochs). and thazt this singular nomenclature is owed to Sir John Menteith (c. 1275–c. 1329), the 'fause [false] Menteith', who in 1305 handed William Wallace over to the English for execution. The connection is unlikely, as the body of water was called Loch Menteith until the nineteenth century, when the Ordnance Survey adopted the misunderstanding by a Dutch cartographer of the Scots laich o Menteith, or 'the low place of Menteith'. Most bodies of water in Scotland that have the name 'Lake' are man-made.
- In Ireland, the convention is to spell the word lough. It is pronounced the same way, and is etymologically indistinguishble. When this word is used in England, as it is sometimes in Cumbria and Northumbria, it is pronounced 'loff', IPA: /lɒf/. (Note that the surname may be pronounced 'luff' or 'low', /lʌf/ or /ləʊ/.)