Relating to a tenth part or to something of great size or significance, especially in Roman military or administrative contexts.
From Latin decumanus, derived from decum- (ten). In Roman times, a decuman gate was the main gate of a camp, and decuman often meant 'of great importance or size.'
Roman soldiers had a 'decuman gate' at their camps—it was the main entrance that everyone went through, and calling something 'decuman' meant it was worth one-tenth of something important.
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