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pair; couple; set
antithesis
counter for items that come in pairs
counter for sets (of clothes, small furniture, utensils, etc.)
一対一で勝負することにしたよ。
I decided to compete one-on-one.
対等な立場で話し合いたいんだ。
I want to talk on equal terms.
この問題に対して意見を述べた。
I stated my opinion on this issue.