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1.
A time one proclaims that they are ready for the job and task ahead.
Ted Kennedy says Barack Obama will be ready to be President from day one.
by Warren Wordsfore February 02, 2008
 
2.
The worst map on Gears Of War 2, it is chosen by noobs and has awkward gameplay for all modes.

It should never be chosen during online play
oh wtf who voted Day One!

oh damn it tied and we have to play day one, long to that!
by I Am Marcus Fenix April 29, 2009