Where does “三角定規” come from?

三角定規 (Japanese) comes from Japanese 三角, from Japanese 三, from Middle Chinese さん.

三角定規 (Japanese): a set square; a triangle

Definitions

  1. a set square; a triangle

Ancestry of “三角定規”, step by step

三角定規 traces back through two separate lines of ancestry.

via Japanese 三角

StepLanguageWordMeaning
1Japanese三角triangle
2Japanese三three, 3; third; three
3Middle Chineseさん—

via Japanese 定規

StepLanguageWordMeaning
1Japanese定規straightedge instrument for drawing lines
Every word from Middle Chinese さん →Every word from Japanese 三 →Every word from Japanese 三角 →