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Femtometre
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<p>The femtometre (American spelling femtometer), symbol fm, (derived from the <a href="/facts/Danish_language/sTcGXTMJ">Danish</a> and <a href="/facts/Norwegian_language/TGEyeerM">Norwegian</a> word <i>femten</i> 'fifteen', <a href="/facts/Ancient_Greek_language/LIK7NlUh">Ancient Greek</a>: μέτρον, <a href="/facts/Romanization_of_Ancient_Greek/KTELT9Aq">romanized</a>: <i>metron</i>, <a href="/facts/Literal_translation/0cF1oFRh">lit.</a> 'unit of measurement') is a unit of <a href="/facts/Length/EwFyAqGH">length</a> in the <a href="/facts/International_System_of_Units/S7YLglNz">International System of Units</a> (SI) equal to 10−15 <a href="/facts/Metre/hPhzc1CV">metres</a>, which means a quadrillionth of one metre. This distance is sometimes called a fermi and was so named in honour of Italian naturalized to American physicist <a href="/facts/Enrico_Fermi/cmYcY15H">Enrico Fermi</a>, as it is a typical length-scale of <a href="/facts/Nuclear_physics/fzQbt1aF">nuclear physics</a>. </p>