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When you have just taken to many drugs over the weekend, its sunday night work starts tomorrow and you are paronoid and depressed the underbus picks you up.
Went a bit mad last night im on the underbus today.
by Mark Lyons November 18, 2006
The act of disowning a close political ally, advisor, or family member who says or does something endangering a candidates election chances
Wow, it sure didn't take Obama long to underbus Wright!

Yeah! Even faster than he underbussed his Grandma. . .
by Wind Rider September 30, 2008
A new way of saying Tube/underground when relating to trains. because an underground train is just an underground bus, or an *underbus*
I will get a bus then I will get the Northern Line on the underbus from waterloo
by Sophierules March 22, 2007