a long, narrow and deep lake in the Highlands of Scotland. It is famous for the Loch Ness monster, also known informally as Nessie. The monster is thought by some people to be a large animal like a dinosaur (= an animal that lived millions of years ago) that spends most of its time underwater. Many people claim to have seen it, and there is a special Loch Ness Monster Exhibition Centre for tourists on the edge of the lake. However several scientific investigations have failed to find any evidence that it exists.