Tekeli-li is a mysterious cry first encountered in Edgar Allan Poe's only novel, "The Narrative of Arthur Gordon Pym" (1838), uttered by the inhabitants of a strange polar island and echoed by white birds. Poe never explained its meaning.
Lovecraft consciously reappropriated the phrase in "At the Mountains of Madness," recasting it as the vocal emanation of the shoggoths. The gesture absorbed Poe's unresolved horror into the Mythos and acknowledged Poe as a foundational precursor.