blow off steam, to

To let out one’s frustration or anger, usually by shouting. The term comes from the early days of railroading, when locomo- tives had no safety valves. When the steam pressure built up, the engineer would pull a lever that would blow off steam and prevent an explosion. It was transferred to human wrath in the early nineteenth century. “The widow . . . sat . . . fuming and blowing off her steam,” wrote Frederick Marryat (The Dog-Fiend, 1837). See also LET OFF STEAM.