Damaged or ruined so as to be unfit for use, or excessively indulged and badly behaved (especially children).
Past participle of 'spoil' from Latin 'spoliare'; British spelling of 'spoiled'; the behavioral sense arose from 18th-century ideas about indulgence ruining character.
British English kept the older past tense 'spoilt' (like 'spilt'), while American English modernized to 'spoiled'—it's a living split in how two dialects evolved their verb systems.
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