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3.
lepton n. (Brit.)(slang) pl. leptons

A mythical measure of velocity used primarily to describe how fast you were travelling in a car. Typically one lepton may or may not equal 10mph or 100mph or 2.734295mph.

Used so that people can post in the public domain how fast they were going, but due to the use of the mythical unit, proof of speed for prosecution purposes is unlikely by law enforcement.
The other day I managed to drag off a Porsche, he stayed with up until about 15 leptons I began to leave him behind.
by Esprit September 03, 2007
 
1.
One of a group of subatomic particles including the electron and neutrino. Leptons, along with quarks, are currently thought to be the ultimate building blocks of nature.
There are six different types of quarks and six leptons.
by OneBadAsp October 21, 2006
 
2.
Z particle. Smaller than protons and electrons.
Woman: What did you just call me?
Child: A Lepton
Woman: What the hell is that?
Child: You wouldn't understand.
Woman: No, speak slowly..
Child: A lepton is a Z particle.
Woman: So?
Child: Do you know what protons and electrons are?
Woman: Yeah.
Child: OK, what are they?
Woman: They're those teeny tiny things atoms are made out of.
Child: Well, leptons are even smaller.

(Shakta - Lepton Head Pt. III)
by Dracus December 20, 2003