adversary

好敵手

an opponent who is good enough to be respected

尊敬に値するほど優れた相手

手ごわい敵

describes an opponent who inspires respect through being impressively powerful or capable

その印象的な強さや能力によって尊敬の念を抱かせる相手を表す

古くからの敵

someone who has been an opponent for a long time

長年の敵である人

恐ろしい敵

describes an opponent who is frightening and powerful

強力で威圧的な相手