The Unnamable by H.P. Lovecraft

"The Unnamable" is a horror short story by American author H. P. Lovecraft. It was written in September 1923, first published in the July 1925 issue of Weird Tales, and first collected in Beyond the Wall of Sleep.
Carter, a weird fiction writer, who is likely the Randolph Carter who features in some of Lovecraft's other tales such as The Statement of Randolph Carter, meets with his close friend, Joel Manton, in a cemetery near an old, dilapidated house on Meadow Hill in the town of Arkham, Massachusetts. As the two sit upon a weathered tomb, Carter tells Manton the tale of an indescribable entity that allegedly haunts the house and surrounding area. He contends that because such an entity cannot be perceived by the five senses, it becomes impossible to quantify and accurately describe, thus earning itself the term unnamable.