Slightly ill or unwell, or unwilling and reluctant to do something.
From the prefix 'in-' (not) plus 'disposed' (inclined or ready). The Latin root 'disponere' means to arrange or incline. The term originally meant 'not arranged favorably' and evolved to describe someone not in the proper state for action.
In polite British society, saying you're 'indisposed' is a genteel way to say you're sick without being gross about it—and it's been used this way for centuries! It's the ultimate upper-class understatement, like saying the Titanic had 'a small leak problem.'
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