Weapons that have been sharpened to a single atom are a particular type of Absurdly Sharp Blade that are so sharp, their cutting edge can be measured in terms of atoms or molecules, often being just a single molecule wide. This usually gives the weapons Absurd Cutting Power, but generally requires the blade to be made out of some sort of Unobtanium to maintain that sharpness without dulling instantly (or just shattering into a million pieces) the first time it's used. For these reasons, the trope is most frequently encountered in Science Fiction settings.