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to collect; to gather; to save; to accumulate; to pile up
宿題が溜まってしまいました。
My homework has piled up.
洗濯物が溜まっていて週末に洗う。
The laundry has accumulated.
読みたい本が溜まっているが、時間が足りない。
Books I want to read have piled up, but I don't have enough time.