Fetching details from the dictionary...

rival; opponent; adversary; competitor; enemy (esp. one with which there is longstanding enmity); foe
revenge
敵の動きを注意深く観察した。
I carefully observed the enemy's movements.
主人公は最終話で父の敵を討った。
In the final episode, the protagonist took revenge for his father.
彼は私にとって手ごわい敵だ。
He is a formidable enemy to me.