The cat-sìth (Scottish Gaelic: [kʰaʰt̪ ˈʃiː], plural cait-shìth), in Irish cat sí (Irish: [kat̪ˠ ˈʃiː]), is a fairy creature from Celtic mythology, said to resemble a large black cat with a white spot on its chest.

The legends surrounding this creature are more common in Scottish folklore, but a few occur in Irish.

Some common folklore suggested that the cat-sìth was not a fairy, but a witch that could transform into a cat nine times.

[5] It is described as being as large as a dog and chooses to display itself with its back arched and bristles erect.

The ceremony required practitioners to burn the bodies of cats over the course of four days and nights.