adverb
Used when something happens again, often with a nuance of mild exasperation or inevitability. Similar to また, but slightly more emphatic or colloquial.
彼はまたぞろ遅刻した。
He was late yet again.
またぞろ雨が降り出した。
It started raining once more.
また is the standard word for 'again'; またぞろ is more emphatic and often carries a nuance of 'here we go again' or mild annoyance.
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.