American Heritage Dictionary
(2)
Century Dictionary
GNU Webster's 1913
WordNet
(1)
Elsewhere on the web
Cigital of Washington DC, he looked at 103 million hands of Texas hold 'em played at the PokerStars online site and calculated how many were won as the result of a "showdown" - in which players win thanks to their cards beating their opponents 'cards - versus those that were won because all the other players folded.— New Scientist - Online News
And I see a glimmer of hope that a showdown could be avoided.— Money and Markets: Free Investment Email Newsletter
The widespread sense on Parliament Hill is that a showdown will be averted.— Thestar.com - Home Page
The showdown was the result of simmering tensions between different groups of students at Hazelwood East High School, prosecutor Doug Sidel said.— STLtoday.com Top News Headlines
I'm told Voxonic can bring Tupac and Notorious B.I.G. back to life for an MC showdown, at least vocally.— ScrippsNews - current events, culture, commentary, community

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You can expect to see this word about twice a week.