Obi

/ˈəʊbi/

noun

noun: obi; plural noun: obis

a broad sash worn round the waist of a Japanese kimono.

Origin

Old Japanese “𝗼𝐛𝐮” – Japanese “𝗼𝐛𝐢” 

Japanese: from Old Japanese, ‘to wear’.

The only purpose was to keep the kimono wrapped in place and so to the obis were just braided cord to wear a kimono at the beginning.

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Definitions from Oxford Languages Dictionary.