time bomb

noun

1. a bomb constructed so as to explode at a certain time.
2. a situation, condition, etc., resembling such a bomb in having disastrous consequences in the future.

noun

1. a bomb containing a timing mechanism that determines the time at which it will detonate
2. a situation which, if allowed to continue, will develop into a serious problem

A situation that threatens to have disastrous consequences at some future time, as in That departmental dispute is a time bomb just waiting to go off. This term alludes to an explosive device that is set to go off at a specific time. [First half of 1900s]