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(a) little; somewhat; somehow
なんだか今日は体がだるくて集中できない。
I feel somewhat sluggish today and cannot concentrate.
なんだか嫌な予感がして早めに帰宅した。
I had a bad feeling for some reason and went home early.
彼の話を聞いてなんだか切ない気持ちになった。
After hearing his story, I felt somewhat wistful.