interjection
It's nothing!; Don't mention it!
Colloquial interjection used to brush off thanks or downplay a minor matter, similar to 'no problem' or 'think nothing of it'.
「手伝ってくれてありがとう。」「なんのなんの。」
"Thanks for helping." "It was nothing."
「ごちそうさま。」「なんのなんの、また来てね。」
"Thanks for the meal." "Don't mention it, come again."