The sometimes slow, sometimes overnight, always surprising transformation of someone, usually a man, from decidedly unattractive to hot as hell a la Matthew Lewis, the actor who played Neville Longbottom in the Harry Potter film series.
“Man, Thomas really Longbottomed that summer after high school and now he’s totally fuxable.” “Whatever bitch, he’s actually too good for you now.”

“Taryn Manning really reverse-Longbottomed to Pennsatucky in Orange is the New Black.”

Matthew Lewis, after the original Longbottoming, is now more attractive than all of his former castmates.”
by Punter Scheisse June 24, 2014
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When a person goes from being a weak nerdy or unattractive person and then suddenly becomes remarkably attractive.
Can also describe someone becoming very badass.
"Hey did you see the trailer for How to train your dragon 2?"
"Nah i havn't why?"
"Hiccup totally gets Longbottomed!"
by NZcountryboy July 21, 2013
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The moment you are left awestruck as a BAMF/knight in shining armor turns out to of been that nobody, clumsy fumbling geek you once knew.
Neville Longbottom
Before(Book 1): Clumsy, forgetful, few to no close friends, toad for a pet

After(book 7):
1. He killed Nagini, Voldemort's snake, with the Gryffindor sword, whilst his head ablaze.
2. Stood up to Voldemort, saying boldly he wouldn't join them until 'Hell freezes over'.
3. He kept recruiting Dumbledore's Army even after Harry, Ron and Hermione had left.

I just saw 'Hiccup' in How to Train Your Dragon 2... Longbottomed again!
by etilauqa July 18, 2013
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Polar opposite of flanderization. When a shallow, bumbling, pathetic, and/or annoying character in a story evolves into a deep, capable (if not extraordinary) hero.
Longbottomed originates from the character Neville Longbottom (from the Harry Potter series), who started in book one as a clumsy comic relief who fell off his broomstick, and evolved throughout the series in terms of character development and competence into a vengeful white knight who slew Voldemort's living snake Horcrux while on fire.
by TheAllKnowingOne February 28, 2014
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v.) an unpopular, bumbling, pathetic person who underwent an extreme personality change, becomes physically attractive, and (sometimes) a BAMF

Derived from the character Neville Longbottom in the Harry Potter series.
A: Is that Mike?!
B: Yeah it's him.
A: OMG really? How did he—
B: He got longbottomed.
by bottomsupniqqa August 2, 2013
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Someone who has successfully navigated puberty like Neville Longbottom in the Harry Potter films.
Daniel Radcliffe: Wow, you've really longbottomed

Matthew Lewis: Yea, I'm really glad I lost the baby fat and can pick up chicks now.
by HollyNoGoLightly November 10, 2015
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The act of simultaneously taking a shit, pissing and ejaculating.
Last night I picked up this really hot chick, when I got her home she totally made me longbottom. There was shit and piss everywhere!!
by Richard Cloutier December 26, 2011
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