1. have power;become law生效
The system of conscription has been in force for many years. 征兵制度已經實行好多年了。
The treaty shall remain in force for a period of ten years. 這條約的有效期為10年。
New timetable is in force. 新的時間表現在生效。
2. a great number of;in a large group大批;大量
The enemy is in force behind the hill. 敵人在山後集結了大量兵力。