1. A poisonous spider.
2. A disingenuous woman who exploits her position in a relationship to the detriment of her partner.
3. In the conflict between Russia and Chechnya, a Chechen widow whose husband died at the hands of the Russians and who consequently becomes a terrorist, usually a suicide bomber, herself.
Example of #3: Authorities found that several of the terrorists involved in the Beslan school massacre were so-called "Black Widows."
An unexpected, dramatic last-minute event which potentially alters the outcome of an election. The term dates to the 1980 presidential campaign, in which Jimmy Carter planned, for October of that year, an operation to rescue American hostages held in Iran. Carter was lagging behind in polls and a successful rescue, an "October surprise," would likely have shifted the momentum to his side. The attempt failed, however, and Carter lost the election. Some have suggested that the Reagan campaign deliberately sabotaged the effort in order to bolster his candidacy.
Before Osama bin Laden released his newest tape, some people thought the Bush campaign would produce him as an October surprise.
A colloquial expression used in simile-like grammatical constructions to attribute particular force to the action of a verb. To state that something is happening "like nobody's business" suggests that it is happening with a particularly high degree of intensity.
It's raining outside like nobody's business!