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So far the majority of you are incorrect.
420's origin IS known.
the term 420 originated at San Rafael High School, in 1971, among a group of about a dozen pot-smoking wiseacres who called themselves the Waldos, who are now pushing 50. The term was shorthand for the time of day the group would meet, at the campus statue of Louis Pasteur, to smoke pot. Intent on developing their own discreet language, they made 420 code for a time to get high, and its use spread among members of an entire generation.
So there ya go, someone's parents out there invented the term 4/20.
And remember this:
There are NOT 420 chemicals in Weed. It's about 315, the num. goes up or down depending on what you're smoking.
4/20 is NOT police code or Maryjane.
And that whole shit about Holland and 4/20 over there being "tea time" for smokers isn't true either.

I know my shit.
by Brandy. April 18, 2003
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In 1971, a group of stoners at San Rafael High School, California, coined this word. It was originally 420 Louis, meaning they planned to smoke weed by the Louis Pasteur statue by their school (btw Louis Pasteur was a hygene expert just fyi) and they said it as like a code word so that they could talk about weed around their parents / teachers and they would not know what the hell they were going on a bout!!! They may have been trying to track down a hidden crop aswell, although that is a bit debated and may be in fact an urban myth. But hey, this is Urban Dictionary, so yea! And then the phrase gained use thanks to the Greatful Dead who publicised it in the 70s and 80s. Today, 44 years down the track, the Waldos are given full credit for coining the term and it still means weed. It is mainly used for fun, secrecy, ritual and protest. A lot of people who smoke weed have a lot of fun with this word, and nobody else really knows wtf they are saying! ... (except their hippy parents!!!!!!! lol oops!)
Oh hey dude, there was this one time at Dennys, I was like super super stoned, I think it might have been after 420!

420 is both a time and a day - It's 4:20 (20 past 4)), or Happy 4/20 (20th of April)

Let's go out on 420 at 420 for some 420ing!!!!!!!!
by sagibitchascent420 February 02, 2016
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4
Common misconceptions point to crazy theories about weed but the truth is it is actuly a number between 419 and 421.
Guy 1: I counted to 420 today!
Guy 2: Sooo you want to get stoned?
Guy 1: What? What the fuck does that have to do with anything?
by Toxic Ninja October 27, 2006
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5
national weed smoking day. light em up at 4:20 pm or am.
man, i cant wait for 4-20 to come. its almost as good as christmas.
by ... April 24, 2005
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6
Supposedly "420" was a code used by the San Rafael police department, however, the department has always denied this. A group known as the "Waldos" claim to have originated 420 in San Rafael in 1971. The group met every day at 4:20 PM after school and eventually began to use 420 as a code for marijuana so they could talk about pot in front of parents and teachers.
Can't wait til 420, I'm going to blaze out of my mind.
by Drew April 04, 2004
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One of the many names for weed. Its mainly in reference to time. But theres also April 20th.
Its 4:20, gota hit that bowl.
I cant wait til 4/20,(april 20th) Im gona be stoned off my ass.
by Sonja February 18, 2003
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