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back
reverse; rear side; back (e.g. of a chair); spine (of a book)
height; stature
ridge (of a mountain)
兄は脊がとても高い。
My brother is very tall.
脊中が少し痛くなってきた。
My back is starting to hurt a little.
猫が脊を丸めて暖かい場所で寝ているよ。
The cat is curled up sleeping in a warm spot.