Where does “काहु” come from?

काहु (Old Hindi) comes from Sanskrit कक्षे, from Proto-Indo-Aryan káṭṣas, from Proto-Indo-Iranian káćšas, from Proto-Indo-European koḱs- — joint.

Ancestry of “काहु”, step by step

StepLanguageWordMeaning
1Sanskritकक्षेin the armpit
2Proto-Indo-Aryankáṭṣas—
3Proto-Indo-Iraniankáćšasarmpit
4Proto-Indo-Europeankoḱs-joint
Every word from Proto-Indo-European koḱs- →Every word from Proto-Indo-Iranian káćšas →Every word from Proto-Indo-Aryan káṭṣas →