彼は私の商売敵だ。
He is my business rival.
彼は長年の敵だ。
He is my longtime enemy.
Used in set phrases like 敵を討つ (かたきをうつ) 'to avenge someone' or 敵討ち (かたきうち) 'revenge'.
父の敵を討つために旅に出た。
He set out on a journey to avenge his father.
Archaic usage meaning 'spouse'. Not used in modern Japanese.
古文では「敵」が配偶者を指すことがある。
In classical literature, 敵 can refer to a spouse.
He kept training with the sword in order to avenge his father.
If you talk like that, you'll end up making everyone your enemy.
rival in go; go opponent