He is my business rival.
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'.
He set out on a journey to avenge his father.
Archaic usage meaning 'spouse'. Not used in modern Japanese.
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.
For people, including opponents in some contexts, but this noun is usually not counted with a standard object counter.
Standard kanji spelling for the reading かたき.
Alternate kanji spelling, often used in the context of revenge or longstanding enmity.
The reading かたき is of native Japanese origin. The kanji 敵 and 仇 are both used to represent the concept of an enemy or rival.