The act of dismissing or ignoring someone, or the release of steam or pressure; can also mean a test that vents excess pressure.
From 'blow' + 'off' (away, separate). Originally a mechanical term for releasing pressure, extended to social meaning of dismissal in 20th century.
Engineers use 'blowoff' valves to prevent explosions in engines, but we use 'blowoff' socially when someone dismisses you—both meanings capture the idea of sudden, forceful separation!
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