Where does “う段” come from?

う段 (Japanese) comes from Japanese 段, from Chinese 段.

う段 (Japanese): the third and middle-graded column of the 五十音図, consisting of the nine kana う/ウ, く/ク, す/ス, つ/ツ, ぬ/ヌ, ふ/フ, む/ム, ゆ/ユ and る/ル, and sometimes additionally 𛄟/𛄢

Definitions

the third and middle-graded column of the 五十音図, consisting of the nine kana う/ウ, く/ク, す/ス, つ/ツ, ぬ/ヌ, ふ/フ, む/ム, ゆ/ユ and る/ル, and sometimes additionally 𛄟/𛄢

Ancestry of “う段”, step by step

う段 traces back through two separate lines of ancestry.

via Japanese 段

Step	Language	Word	Meaning
1	Japanese	段	steps (up and down); stairs
2	Chinese	段	—

via Japanese う

Step	Language	Word	Meaning
1	Japanese	う	Used to make the volitional form of verbs;...
2	Middle Chinese	羽	—

Every word from Chinese 段 →Every word from Japanese 段 →