somebody who's really, really old... "older than dirt" old
Timmy's grandad is named Methuselah!
by Super Guy February 20, 2004
A fictitious race of Vampires from the show Trinity Blood. They are named Methuselah's after the Biblical man of the same name who lived to almost a thousand years.
Methuselah's are vampires; Terrans are regular humans.
by DannoRly November 16, 2007
When one farts in the shower and the surrounding moisture/heat causes the stench to become more intense and linger in a most disgusting manner.
Dude I was in the shower with my girlfriend and she unleashed a methuselah that almost made me vom.
by Penis Goblin November 27, 2010