He was accused of collaborating with the enemy during the occupation.

collaborating 是动词 collaborate 的现在分词形式。collaborate 由前缀 col-（表示"共同"）和 labor（劳动）组成，字面意思是"共同劳动"，引申为"合作"。但在负面语境中特指"与敌方勾结"。