noun, adverb
many days; for days on end
Formal or literary word for a period of many days, often used in written language or formal speech. Can function as a noun or adverbially.
累日の雨で川が増水した。
The river rose due to many days of rain.
累日にわたる協議の末、合意に達した。
After many days of discussion, they reached an agreement.