verb
to gather or summon (a group of people), especially for a specific purpose
adverb
used to emphasize the effort or determination required to do something
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She had to muster up the courage to give a presentation in front of the board.
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I had to muster up the energy to go to the gym after work.
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I couldn't muster up the motivation to study for the exam.
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He tried to muster up a smile despite feeling sad.