A square paving stone or tile, or in medieval times, a short wide-headed arrow or crossbow bolt.
From Old French 'carreau' meaning 'square', derived from Latin 'quadratus' (square). The word has multiple meanings depending on context and time period.
Medieval soldiers feared carreaus as crossbow ammunition—they were devastating short arrows that could pierce armor—but the same word later meant ordinary floor tiles because of the square shape.
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