Capable of being demanded, required, or collected, especially in reference to taxes or payments.
From exact (verb) + -able. Exact comes from Latin exactus 'driven out, completed' (past participle of exigere), which evolved to mean 'precise' and 'to demand/collect.'
Medieval tax collectors loved precision—the word 'exact' originally meant to drive something out or extract it, which is exactly what tax collectors do with your money.
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