cause of trouble; root of misfortune
A somewhat formal or literary noun for the underlying cause of a problem or disaster. Often used in analytical or explanatory contexts.
The failure of that policy became the cause of the turmoil.
He analyzed the root causes of the organization's decline.
Compound of 禍 (calamity) and 因 (cause). The exact historical derivation is uncertain, but the word follows a standard Sino-Japanese compounding pattern.