The Spanish word 'duro' meaning 'hard' comes directly from the Latin word 'durus', which meant 'hard' or 'firm'. This is a straightforward inheritance where both the form and meaning have remained remarkably stable over time from Latin to Spanish.

Several common Spanish words are built from 'duro', including: 'dureza' (hardness), 'durar' (to last/endure), and 'durante' (during). The connection between hardness and duration comes from the idea that hard things tend to last longer or endure more.

English has borrowed several words from the same Latin root 'durus'. The most common ones include 'durable' (able to last a long time), 'endure' (to last or suffer through), and 'duration' (length of time). The word 'duress' (forceful restraint or coercion) also comes from this root, reflecting the hardship or hardness implied in the original Latin meaning.