What it means
An unpredictable person or factor whose moves nobody can call, borrowed from card games where one card can stand in for any other. A wild-card candidate might surprise everyone, for better or worse. The fun and the danger both lie in not knowing which way they will jump.
Usage examples
"He is the wild card of the negotiation, charming one minute and storming out the next, so plan for anything."
"Nobody knows how he'll vote, he's the wild-card on the committee."
"The weather is the wild-card for Saturday's match, could go either way."
Where it comes from
Borrowed from card games, where a wild card can stand in for any other in the deck. Applied to people or events, it marks the unpredictable one whose move nobody can call, full of both promise and risk.
Other ways to say it
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