Refers to the reason, origin, or background behind something, often implying a historical or logical connection. Can also mean a relationship or affinity between people or things. Slightly formal/literary.
I'm researching the origin of this town's name.
The reason he's called 'Iron Man' lies in his incredible stamina.
Standard kanji spelling. Often used in formal or literary contexts.
Kana spelling is common in everyday writing, especially when the kanji are considered difficult.
Composed of 由 (reason, cause) and 縁 (connection, edge). The combination emphasizes a causal or relational link. The exact historical derivation is uncertain, but the kanji are conventionally associated with the meaning.