名詞 time bomb:

1. a problematic situation that will eventually become dangerous if not addressed
   同義詞：ticking bomb
2. a bomb that has a detonating mechanism that can be set to go off at a particular time
   同義詞：infernal machine

1. The criminal has admitted to putting the time bomb inside the railway station.
   罪犯已供認是他把定時炸彈安放在火車站里的。