Boojum (n)
from the OED:
“[Invented by ‘Lewis Carroll’ (C. L. Dodgson) in The Hunting of the Snark (1876).]
An imaginary animal, a particularly dangerous kind of ‘snark’.
1904 B. VON HUTTEN Pam III. vi. 146 We shall see a good deal of each other. I am a boojum, and I know. 1922 Edin. Rev. Oct. 241 Both these beautiful abstractions are in reality boojums. 1925 Blackw. Mag. Mar. 345/1 A solitary Boojum-like person. 1950 AUDEN Enchafèd Flood (1951) i. 42 The dreadful Boojum of Nothingness.”
Famous boojums include:
Biblioklept 