you could have knocked me down with a featheridiomPart offeatheryou could have knocked me down with a featheryou could have knocked me down with a feather — idiomidiom1. Used to show that you were extremely surprised by something.1.idiomDefinitionUsed to show that you were extremely surprised by something.ExampleWhen Aiden won the lottery, you could have knocked me down with a feather.You could have knocked me down with a feather when I saw the final score.