Where does “tri-armed” come from?

tri-armed (English) comes from English armed, from English Arm, from Middle English arm, from Old English earm, from Proto-West Germanic arm, from Proto-Germanic armaz, from Proto-Indo-European h₂ermos, from Proto-Indo-European h₂er- — to fit, to fix, to put together.

Ancestry of “tri-armed”, step by step

tri-armed traces back through two separate lines of ancestry.

via English armed

StepLanguageWordMeaning
1EnglisharmedEquipped, especially with a weapon; Prepared for...
2EnglishArmAbbreviation of Armenian
3Middle Englisharmarm; poor; miserable, wretched
4Old Englishearmarm; poor, miserable
5Proto-West Germanicarmarm; poor, miserable; pitiful, pitiable
6Proto-Germanicarmazarm; poor, miserable; pitiful, pitiable
7Proto-Indo-Europeanh₂ermos
8Proto-Indo-Europeanh₂er-to fit, to fix, to put together

via English tri

StepLanguageWordMeaning
1Englishtritriathlon; triangle
2Proto-Indo-Europeantréyesthree
Every word from Proto-Indo-European h₂er-
tri-armed — Etymology, Origin & Word History | Etymology Explorer