Something or someone that is lightning-quick is, figuratively, as quick (as fast and agile) as lightning. Ex.: "That hockey team's center is lightning-quick! He can score goals before you even know he's there." Can be written "lightning quick" (two words). Equivalents: Quick as a flash; quick as a wink; quick as lightning. All of these mean the same thing; the only thing that changes is how the idea is conveyed.