Cord material collectively, or the act of binding or tying with cord; also refers to the raised lines of muscle or veins visible on someone's skin.
From the verb 'cord' (to bind with cord) plus the gerund suffix '-ing.' The term has been used since the 15th century for both the material and the action.
When people describe muscular veins and muscles as 'cording,' it's because intensely fit individuals can develop such prominent cordlike structures under the skin that they literally look like they have ropes running through their forearms!
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