From Longman Dictionary of Contemporary Englishknockoutknock‧out1 /ˈnɒk-aʊt $ ˈnɑːk-/ noun [countable] 1 DSOwhen a boxer hits his opponent so hard that he falls down and cannot get up again The fight ended in a knockout.2 informalBEAUTIFUL/GOOD-LOOKINGSEXY someone or something that is very attractive or successful Her dress was a knockout.3 COMPETE WITH/TRY TO BEATa type of competition in which only the winning players or teams at each stage continue to play until there is only one winner
Examples from the Corpus
knockout• Rated G.. Toy Story A knockout.• Sunday's concert was a knockout.• She was a knockout in gym shorts.• A fight could end three ways: by knockout, surrender or by intervention of the referee.• Leslie's a real knockout.• Barrera won by an eighth-round knockout but Cook frustrated him at times.• It leaves the ring on a stretcher; the result is a first-round knockout.knockoutknockout2 adjective informal 1 → knockout punch/blow2 relating to a type of competition in which only the winning players or teams at each stage continue to play Scotland’s failure to get through the knockout stage of the competition3 → knockout pills/drops etcExamples from the Corpus
knockout• The piece opens and closes with knockout ensemble dances.• The knockout loss to Lewis, which came in the sixth round, seemed to put him out of title contention.• Obese mice, diabetic mice, musclebound mice, even knockout mice.• He may not have a knockout punch, but he does have good moves all the way to the bell.• It was a knockout punch of which Indurain, Hinault or Merckx would have been proud.• He insisted there was some-thing about his right hand-the hand that delivered the knockout punch-that was strange.• That seven eighty-one was like a knockout punch.• Wenger's Arsenal are on the brink of breaking into the knockout stage at the third time of asking.From Longman Business Dictionaryknockoutknock‧out /ˈnɒk-aʊtˈnɑːk-/ noun [countable] an arrangement in which people who are trying to buy the same thing agree not to compete against each other on the priceIt appears to be doubtful whether a knockout was arranged.aknockout agreement 