The Japanese word for enemy is
敵

てき - teki

Japanese Definition

enemy
1. 名詞. 敵。
He made a lot of enemies after reducing the working hours in his department.
Crush the enemy!
2. 名詞. 敵国、敵軍。
rally together against a common enemy.
3. 名詞. 反対者。
4. 形容詞. 敵の、敵に関する。

敵
1. n. an enemy
2. n. revenge, vengeance
(ja-x, 親の敵, おやのかたき, revenge for one's parent's death)
3. n. opponent (of the game or conflict)
4. n. (from early 1200s) an enemy
5. n. (from early 1800s) an opponent, a competitor
敵を倒す - defeat an opponent
6. n. (1466–???) (historical) the other party in a lawsuit
7. n. (from 1678) 的: (historical) in the red-light district, a term of reference used between prostitutes and customers
8. pron. (from 1811) 的: (historical) q, by extension from the red-light district usage (term of third-person reference): that guy, that one
(synonyms, ja, やつ, tr1=yatsu)
9. pron. (from 1809) 的: (historical mildly, derogatory) q, by extension from the red-light district usage (term of second-person reference): you
(synonyms, ja, お前, tr1=omae)