peacock's tail
/ˌpiːkɒks ˈteɪl/noun
1The tail coverts of a peacock collectively, which the bird is able to erect and expand like a fan behind its body..
2 Alchemy. An iridescent or multicoloured stage in the preparation of the philosopher's stone. Now historical.
3The seaweed Padina pavonia, which has broadly fan-shaped fronds marked with fringed bands in shades of brown and green.
Origin
Early 16th century. From the genitive of peacock + tail. In β form from peacock + tail.