Third person singular of decay; to rot, decompose, or gradually deteriorate over time.
From Old French 'decair' meaning 'to fall down,' from Latin 'decidere' (de- 'down' + cadere 'to fall'). The sense evolved from physical falling to gradual deterioration by the 14th century.
Decay is essentially time made visible - whether it's a fallen log becoming soil or a abandoned building crumbling, it's the universe's way of recycling everything back to its basic components. Scientists now know that even protons might decay, meaning nothing truly lasts forever.
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