noun
primary factor; main cause
Used in analytical or explanatory contexts to identify the most important reason or element behind a situation. Often contrasted with 副因 (secondary factor).
See also: 要因
事故の主要因はスピードの出し過ぎだった。
The primary factor in the accident was excessive speed.
この問題の主要因を特定する必要がある。
We need to identify the main cause of this problem.
副因 refers to a secondary or contributing factor, often used in contrast with 主要因.
Compound of 主要 (primary, main) and 因 (cause, factor). The reading is on'yomi throughout.