also: あまっさえ
adverb
besides; moreover; on top of that; to make matters worse
Dated adverb, usually with a negative nuance. Adds an additional, often unfavorable, point to a situation. Common in written or formal speech.
He was late. On top of that, he forgot his homework.
雨が降り出し、あまつさえ風も強くなってきた。
It started to rain, and moreover, the wind grew stronger.