Used when something happens again, often with a nuance of mild exasperation or inevitability. Similar to また, but slightly more emphatic or colloquial.
He was late yet again.
It started raining once more.
Rare kanji spelling; learners should use the kana form.
Derived from また (again) with the emphatic suffix ぞろ. The exact origin of ぞろ is uncertain, but it may be related to the adverbial suffix ぞろ found in words like うろうろ or のろのろ.