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cartilage
nankotsu; (dish of) gristle (usu. of chicken, deep-fried)
軟骨の唐揚げ、追加でどう？
How about another order of crispy fried chicken cartilage?
膝の軟骨が少し磨り減っていますね。
The cartilage in your knee has worn down a bit.
関節の軟骨は一度減ると元には戻らない。
Once joint cartilage wears down, it doesn't recover.