femtometer
/ˈfɛmtoʊˌmiːtər/
noun
- A unit of length equal to one quadrillionth of a meter (10⁻¹⁵ meters), used in physics to measure atomic nuclei and subatomic particles.
- The radius of a proton is about 0.84 femtometers.
- A femtometer is so tiny that it takes a million of them to span a single nanometer.
- Scientists use femtometers to describe distances inside an atom's nucleus.