• 原因げんいん — cause / origin
• 要因よういん — primary factor
• 因果いんが — cause and effect
• 因習いんしゅう — custom / convention
• 病因びょういん — cause of illness
• 因縁いんねん — fate / connection

The enclosure radical 囗 surrounds 大 (person), interpreted as someone lying down. This suggests passivity — someone being affected or influenced — forming the sense of “cause” or “reason.”

事故じこの 原因げんいんを 調しらべています。
We are investigating the cause of the accident.

因果関係いんがかんけいを 明あきらかにする。
Clarify the causal relationship.