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(a) little; somewhat; somehow
何だか今日は気分が乗らなくて仕事が進まない。
Somehow I'm not in the mood today and work isn't progressing.
彼女の様子が何だかいつもと違うように感じられる。
She somehow seems different from usual.
何だか嫌な予感がするので今日は出かけたくない。
I have a bad feeling for some reason and don't want to go out today.