Impossibly describes something done in a way that seems impossible or like it shouldn't be able to happen. When a gymnast performs an impossibly difficult routine, she executes moves so challenging they seem beyond human ability. When someone is impossibly kind, their generosity exceeds what you'd normally expect from anyone.

The word often expresses amazement or disbelief. A math problem might be impossibly complex, meaning it feels so hard it can't be solved (though usually it can be, with enough effort). A hallway might seem impossibly long when you're rushing to class, or a dessert might taste impossibly good, as if no recipe could create something so delicious.

Notice that impossibly doesn't always mean literally impossible. It's often an exaggeration that captures how extreme something feels. When you say your little brother is impossibly annoying, you mean he's more annoying than seems humanly possible, not that his annoyingness defies the laws of physics. The word adds dramatic emphasis, turning ordinary descriptions into expressions of wonder, frustration, or awe.