1.
root cause, chief culprit, main offender
The primary source of a problem or the person most responsible for causing harm. Carries a strongly negative connotation.
問題の元凶を探す。
Look for the root cause of the problem.
渋滞の元凶は工事だった。
The main cause of the traffic jam was road construction.
長年の不正の元凶となった人物がようやく逮捕された。
The person who was the chief culprit behind years of fraud was finally arrested.
Can refer to both a person (the culprit) and a thing (the root cause). Always used negatively — it implies blame and responsibility for a bad outcome.
COMMON COLLOCATIONS:
- 元凶を突き止める (identify the root cause)
- 問題の元凶 (root cause of the problem)
- 諸悪の元凶 (the source of all evils)