From Longman Dictionary of Contemporary Englishtime bombˈtime bomb noun [countable] 1 PMWSCBa bomb that is set to explode at a particular time2 PROBLEMa situation that is likely to become a very serious problem Cutting down the rainforest is an environmental time bomb.
Examples from the Corpus
time bomb• The Senate version of the bill contained a time bomb, however.• It is a time bomb waiting to explode.• Her footsteps and the faint noise of her limbs striking one another as she walked sounded like the mechanism of a time bomb.• With the rise in teenage HIV infection rates, we are sitting on a time bomb.• Our baby is a bomb, too: a time bomb.• Was it some psychic time bomb long ago planted on Ludlow Street?• The man is clearly a walking time bomb.• I felt like a walking time bomb, set to detonate in sixty minutes. 