"a place of deposit for powder, or some other highly combustible substance,..."See in text(The Fall of the House of Usher)
The presence of the powder hoard directly invokes a dramatic principle known as Chekhov’s gun. Anton Chekhov, the Russian playwright and story writer, wrote in an 1889 letter to a colleague that “One must never place a loaded rifle on the stage if it isn't going to go off. It's wrong to make promises you don't mean to keep.” The implication is that, when handled correctly, such a detail—be it a rifle or a basement full of gunpowder—ought to reappear in a meaningful way later on in the plot.
"the echo..."See in text(The Fall of the House of Usher)
Echoes are a central motif of the story. The echo here is a physical echo within the reality of the story; it is also an echo of the echo in the “Mad Trist” story and also an echo of the echoes in “The Haunted Palace,” the poem within the story. These echoes signify the powerful echoes of history and lineage, as can be seen in the role of the stories and poems within the story which serve to foreshadow the plot. The echoes also represent the atmosphere of the Usher mansion itself, with its eerie, echo-filled hollowness.
"“The Haunted Palace,”..."See in text(The Fall of the House of Usher)
This is a poem by Poe, which is often printed separately from this story. It was first published in April of 1839 but did not find initial success, possibly leading to Poe’s including it in “The Fall of the House of Usher.” The poem relates the events of a king from long ago who fears the evil forces that plague him and his palace. The poem serves as an allegory for the House of Usher, foreshadowing the impending doom Roderick faces.
"so identified the two as to merge the original title of the estate in the quaint and equivocal appellation of the “House of Usher”—an appellation which seemed to include, in the minds of the peasantry who used it, both the family and the family mansion...."See in text(The Fall of the House of Usher)
The noun “appellation” simply means an identifying name or title. In this line, “appellation” is preceded by the adjective “equivocal,” making the meaning clear: the “House of Usher” is the same name and title for both the family and the physical house. As Poe’s narrator continues to say, the peasantry (and readers) see the family and the house as inextricably intertwined—as if they share the same fate.