Definition of "oughts"

He and his clever staff of minor blackguards exploited to the full every weakness and caries in the London Society of the 'eighties, 'nineties, and 'oughts.

1919, Harry Hamilton Johnston, The Gay-Dombeys: A Novel, Macmillan, page 172

And for the oughts—by which I suppose we must identify our new millennium's first decade—projected tonnage figures keep up the mind-boggling pace.

2000, John Maxtone-Graham, Liners to the Sun, Sheridan House, Inc., page xii

The "experts" of the Western world are slower to turn around than an ocean liner, and in Europe they were still yakking about the "population explosion" even as their 1970s schoolhouses, built in anticipation of traditional Catholic birth rates, were emptying through the nineties and oughts.

2006, Mark Steyn, America Alone: The End of the World as We Know It, Regnery Publishing, page 13