one cause; one factor; one reason
Used to indicate one contributing factor among several, often in explanations of events or situations. Common in formal and written contexts.
事故の一因はスピードの出し過ぎだった。
One cause of the accident was excessive speed.
One factor in his success is the support of his family.
Lack of exercise is one factor contributing to obesity.
It is thought that one cause of the accident lies in the driver's carelessness.
The economic slump is one factor behind the rise in unemployment.
Researchers are investigating one of the causes of the disease.
誘因 is a triggering factor that induces an event, while 一因 simply denotes one of several causes without implying it set anything off.