Someone or something, especially a sports team, that defeats a larger and superior opponent.(noun)
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Use "giant-killer" in a sentence
"The visitors played with the togetherness that every giant-killer needs."
"Cricket's governing body faces a dilemma over the game's biggest giant-killer."
"Kim Huybrechts also caused a shock to put out the giant-killer James Richardson, the conqueror of five-times winner Raymond van Barneveld in the first round."