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To summon, gather, or cobble something together. Said especially of intangible qualities, such as courage, determination, etc. Eventually I mustered up the courage to go over and ask him for his phone number. Despite outperforming the other team for most of the game, they were only able to muster up a single goal. Can you muster the strength up to walk back to camp, or should I go for help?
muster something up
to call up some quality, such as courage. Do you think you can muster enough courage up to do the job? Can you muster up enough strength to do the job?
To gather up some force of will to do something: I couldn't muster up the courage to tell them about my terrible mistake. Although the team lost, they mustered some good cheer up and went to the party.