Filled with suppressed anger that bubbles just beneath the surface. It describes intense rage that is being controlled or contained but threatens to explode.
From Old English 'seoþan' (to boil), related to cooking and brewing terms. The metaphorical use comparing anger to boiling liquid developed in the 13th century, capturing the sense of heat and pressure building up.
Seething perfectly captures anger as a physical process - your body literally heats up as stress hormones flood your system, creating that sensation of 'boiling over.' This suppressed rage can be more psychologically damaging than expressed anger because the chronic stress activation wears down both mental and physical health.
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