Third person singular present tense of combust; burns or undergoes combustion.
From Latin 'comburere' (to burn completely), with the modern English third-person singular suffix '-s.' This is the conjugated form used in contemporary descriptions of burning.
When scientists say 'this material combusts spontaneously,' they mean it ignites without an external spark—just exposure to air is enough. Understanding spontaneous combustion saved warehouses from mysterious fires caused by oily rags left to oxidize.
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