Definition of "lighten up" []

• To become less serious and more cheerful or casual; to relax. (verb)

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• "If we cut out the absurd, frivolous use of aluminum as a container for our beverages, we can put the tons of aluminum already in circulation into Stuff that makes sense, like to replace some steel to lighten up our modes of transportation, especially while these are still running on CO2-spewing fossil fuels."