To get significantly more attractive after going through the process of puberty.
Origin stems from Harry Potter, where the character Neville Longbottom (actor: Matthew Lewis) went from a dumpling shaped (but very
sweet) 11 year-old to a daaaamn fine (and still very
sweet) 25 year-old today.
The word was popularised by
tumblr usage as both a noun and a verb.
Me looking in the mirror: I'
d better Neville Longbottom by the time I get to uni, or I'm going to die alone. :/
Person returning home from uni: Is that...? Is that
Susan?! Well she certainly Neville Longbottomed.
Person referring to their boyfriend: Nah, I'm not gonna break up with him. Yeah he'
s kinda pudgy,
bit fingers crossed he'll do a Neville Longbottom!