Past tense of boil; heated liquid to the point where it bubbles and turns to vapor, or cooked food in boiling water. Can also describe intense anger or agitation.
From Old French 'boillir,' ultimately from Latin 'bullire' meaning 'to bubble up.' The metaphorical sense of emotional agitation (boiling mad) developed from the visual similarity between bubbling water and intense feelings.
The phrase 'boiling point' works both scientifically and emotionally because humans have always connected the violent bubbling of heated water with intense feelings! This metaphor appears in dozens of languages, suggesting it's a nearly universal way of understanding anger.
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