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lapse of memory; (something) slipping one's mind; forgetting for a moment something one knows well
人の名前をど忘れしてしまい気まずかった。
I had a momentary lapse and forgot the person's name, which was awkward.
会議で発言する内容をど忘れして焦った。
I panicked when I forgot what I was going to say at the meeting.
暗証番号をど忘れして銀行で手続きが必要になった。
I forgot my PIN number and had to go through a procedure at the bank.