Meaning of なのだ in Japanese

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Definition of なのだ

なのだ(nanoda) · なんだ(nanda)

「親父これって・・・真剣しんけん？」「当たり前あたりまえだろう、決闘けっとうなのだからな」

"Dad, this a real sword?" "Of course, it is a duel after all."

ここだけの話はなしだが彼女かのじょについて君のきみ意見いけんはどうなのだ。

Between you and me, what is your opinion of her?

うちのうち犬いぬは、ジョンという名前なまえなのだが、だれにでも吠えるほえる。

Our dog, which is named John, barks at anybody.

What in the world does he mean?

あの飛行機ひこうきはなんて巨大きょだいなのだろう。

How huge that airship is!

What a little imp he is!

Since you're a member of this sports club, you'll have to conform to its rules.

"I just wish that I could be with you forever and always," replied the little black rabbit.

「邪魔じゃまをしてするはいけないよ。彼女かのじょは今いま、仕事中しごとちゅうなのだから。」と彼かれは小声こごえで言った。

"Don't disturb her. She is at work right now" he whispered.

"This must be living in the city," thought the Little House, and didn't know whether she liked it or not.