Occurring every ten years; relating to a period of ten years.
From Latin decennium (period of ten years), from decem (ten) plus annus (year), plus the adjective suffix -al. Emerged in English as a variant of 'decennial.'
The U.S. Census is decennal—it happens every ten years, and the results reshape how voting districts and federal funding get distributed, which is why some groups get really invested in being counted correctly.
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