A principal enemy or rival, especially one who is particularly hostile.

मुख्य दुश्मन

English Usage: Their entire life was defined by their rivalry as archenemies from childhood.

Hindi Usage: उनका पूरा जीवन बचपन से मुख्य दुश्मनों के रूप में उनकी प्रतिद्वंद्विता द्वारा परिभाषित था।