Chthulu, on the Nefandous Southpark

Nefandous

Unspeakable.

A most severe pejorative

Examples:

Then the earth
In birth nefandous Coeus life produced
And Iapetus and Typhoeus dire
And that bad brotherhood which joined in league
To abolish heaven
— Dante Alighieri, Inferno (1308)

Only the bricks of the chimney, the stones of the cellar, some mineral and metallic litter here and there, and the rim of that nefandous well.
— H.P. Lovecraft, The Colour out of Space (1927)

No Topsman to your Tarpeia! This thing, Mister Abby, is nefand.
—  James Joyce, Finnegans Wake (1939)

Etymology:

• In Latin, ne = not, fandus = to speak