In Welsh folklore, the mine fairies are called coblynau, with coblyn as the singular form. They are gnome-like beings associated with the mines and quarries of Wales.
Coblynau were said to resemble miners, often appearing in work clothes and carrying tools. Their distinctive knocking could be interpreted as a warning of danger—or as a sign pointing miners toward rich veins of ore. This connects them with the wider British tradition of supernatural mining helpers, including Cornwall's knockers.
The word is related to “goblin” and may ultimately reflect Germanic and French forms such as kobold and gobelin. A common mix-up is treating coblyn as the plural name; strictly, coblynau is plural, but coblyn is the standard dictionary headword and is a fair quiz answer for the creature or tradition.