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Phrase(s): get up a (full) head of steam
1. Lit. [for a steam engine] to build steam pressure in order to start operating. • It took nearly thirty minutes to get up a full head of steam so that the locomotive could start moving. 2. Fig. to develop sufficient energy, enthusiasm, commitment, or determination to undertake something. • It’s nearly noon before I can get up a full head of steam and accomplish something.
McGrawhill's American Idioms And Phrasal Verbs