adverb
all night long; all through the night
Adverb describing an action or state that continues throughout the entire night.
昨夜は一晩中雨が降っていた。
It rained all night long last night.
彼は一晩中勉強した。
He studied all through the night.
Compound of 一晩 (ひとばん, 'one night') and 中 (じゅう, 'throughout').