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faint memory; vague memory; dim memory; vague recollection
その時のことはうろ覚えだ。
I have only a faint memory of that time.
うろ覚えでクイズに答えた。
I answered the quiz based on a vague recollection.
彼の話はうろ覚えの知識ばかりだった。
His story was full of vague recollections.