nut up v. to become bold, courageous, or forthright; to sack up, man up. (source: Double-Tongued Dictionary)
Further reading
Samantha Harvey’s novel Orbital is a sensuous, exhilarating meditation about the strangeness of life on a space station, with its mix of tedious tasks and jaw-dropping views. And: a musician who rode the rails in his youth shares the slang he...
A Francophone who’s feeling low might say so with J’ai le moral dans les chaussettes. The idiom avoir le moral dans les chaussettes means “to have morale in your socks.” This is part of a complete episode.
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