The Féth Fíada is a magical mist or veil in Irish mythology, which members of the Tuatha Dé Danann use to enshroud themselves, rendering their presence invisible to human eyes. ‘Féth’ means magical mist and ‘Fíada’ means ‘knower’. The mist is also called ‘ceo draíochta’ meaning magical fog, or ‘ceo druídecta’ meaning druid’s fog.
When An Tuatha dé Danann were defeated by the Milesians and forced underground, they took up residence in the hills and mounds where they rebuilt their homes or ‘sidhe’. Manannán mac Lir was said to have raised the Féth Fíada to conceal them from the mortals.