1.
one cause, a contributing factor
One of several causes or contributing factors. Implies that the cause mentioned is not the only one, but one among multiple factors.
ストレスも病気の一因だ。
Stress is also a contributing factor to illness.
人手不足が事故の一因となった。
A shortage of workers was one cause of the accident.
食生活の乱れが生活習慣病の一因になっていると言われている。
Poor eating habits are said to be a contributing factor to lifestyle diseases.
COMMON PATTERNS:
- ～の一因だ: is a contributing factor of ~
- ～の一因となる: become a contributing factor of ~
- ～の一因になっている: is one of the factors behind ~
NUANCE:
Using 一因 implies the speaker acknowledges multiple causes. It is more measured than 原因 (cause), which can imply a single or primary cause.
FORMALITY:
A somewhat formal word, common in news, academic writing, and analysis.