great disaster; catastrophe; train wreck
Refers to a large-scale, devastating event, often with serious consequences. Can be used literally for natural or man-made disasters, or figuratively for a disastrous situation.
The earthquake caused a great disaster.
His plan ended in a catastrophe.
Compound of 大 (dai, 'big, great') + 惨事 (sanji, 'disaster, tragedy'). The exact historical derivation is uncertain, but the combination straightforwardly intensifies the meaning of 惨事.