What does the word ‘duel’ in the passage mean?

Directions: Read the passage and answer the question.

“Westward Ho !” we shouted as the sail of our crudely constructed raft, the Kon-Tiki caught the wind. The sail quickly filled and the Kon-Tiki began to move. The six of us were off to our great adventure. As night fell, the troughs of the sea grew gradually deeper and our first duel with the elements began. Each time we heard the sudden deafening hiss of a roller close by and saw a white crest come towards us out of the darkness, we held on tight and waited for the worst. But invariably the Kon-Tiki calmly swung up her stern and rose skyward, unperturbed.