Removed the fuse from an explosive device to prevent it from exploding; or reduced tension and danger in a situation.
From 'de-' (to undo) + 'fuse' (the ignition device). Originally a technical term in bomb disposal, then extended metaphorically to mean 'reducing any dangerous situation.'
The phrase 'defuse a bomb' has become so common in describing tense situations that people often use it when they have nothing to do with actual explosives—showing how technical language becomes everyday metaphor!
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