femtometer
noun
fem·to·me·ter
ˈfem(p)-tə-ˌmē-tər 
-tō-
: a unit of length equal to 10−15 meters : one quadrillionth of a meter
Examples of femtometer in a Sentence
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This explains why the proton and neutron have particular sizes to them, where each one has a radius that’s a little smaller than a femtometer.
—
Ethan Siegel,
Forbes,
20 Apr. 2021
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Ethan Siegel,
Forbes,
20 Apr. 2021
Cite this Entry
“Femtometer.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/femtometer. Accessed 5 Jul. 2026.
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