Once you've read "The Pit and the Pendulum," the title seems pretty… obvious. Yes, the story features a pit and a pendulum, and, yes, they're two truly terrible torture devices. So what?
The thing is, in order to really appreciate the title, you have to step back and remember a time when you didn't know what the story was all about (i.e. before you started reading). Neither a pit nor a pendulum is necessarily dangerous, and they also seem totally unrelated. But as it turns out, they're the things that have a shot at killing our precious narrator… yikes.
By putting those two things together in the title, Poe does something pretty cool and pretty strange. For one thing, he creates a neat alliterative phrase ("pit" and "pendulum" both begin with the "p" sound).
More importantly, though, Poe uses his title to create suspense in his story. Sounds strange right? But hear us out. The moment you figure out that the pit is a method of torture, you begin to realize that the pendulum most likely is, too. So now you're anticipating the appearance of the pendulum and, the moment the narrator finds himself gazing up at it, you figure out (probably before he does) that nothing good will come of it. Pretty cool, right?
And, of course, this title is a little subtler than some alternative titles. Would you really want to read a story called "A Scary, Gruesome, Terrible, Horrible Story in Which a Guy Gets Tortured By the Spanish Inquisition"? No? That's what we thought.