durus

Durus, dura, durum is a first and second declension adjective covering hard to the touch, tough in constitution, and harsh in manner. It compares regularly: durior, durissimus. Its opposite is mollis.

Of a Roman politician it is not a compliment. Of Virgil's farmers and soldiers it very much is, and durum genus is praise, which makes the adjective a small nuisance to translate consistently. The abstract noun is duritia and the verb duro means both "harden" and "hold out, last", which is why English duration has nothing whatever to do with hardness. Endure, durable and obdurate all come from the same root.