Where does “riding robe” come from?

riding robe (English) comes from English riding, from English trithing, from Middle English trithing, from Old English þriðing, from Old Norse þriðjungr, from Proto-Germanic þridjô, from Proto-Indo-European tretyós, from Proto-Indo-European tr̥tyós — three.

Ancestry of “riding robe”, step by step

riding robe traces back through two separate lines of ancestry.

via English riding

StepLanguageWordMeaning
1Englishridingpresent participle of ride; A path cut through...
2EnglishtrithingOne of three ancient divisions of a county in...
3Middle Englishtrithing
4Old Englishþriðing
5Old Norseþriðjungrthird part
6Proto-Germanicþridjôthird
7Proto-Indo-Europeantretyós
8Proto-Indo-Europeantr̥tyósthird
9Proto-Indo-Europeantréyesthree

via English robe

StepLanguageWordMeaning
1EnglishrobeA long loose outer garment, often signifying...
2Middle Englishroberobe; The garments an individual is wearing
3Old Frenchrobebooty; spoils; piece of clothing
4Frankishrouba
5Proto-West Germanicraubrape, pillage, robbery; that which is stolen,...
6Proto-Germanicraubōrift
7Proto-Indo-Europeanreup-to break; to tear, peel
Every word from Proto-Indo-European tréyes