He was interned as an enemy alien at the outbreak of the Second World War.

他在第二次世界大战爆发时被作为敌国侨民扣押了。

《柯林斯英汉双解大词典》

"XCOM: Enemy Unknown" is a science fiction, strategy game pitting Earth against an invading alien force.

CNN: Two games in one in 'XCOM: Enemy Unknown'

An alien bug that causes diarrhoea, for instance, is as much an enemy of the microbiome as of the host.

ECONOMIST: Modern medicine