all night long; throughout the night
Literary or formal noun meaning the entire night. In modern Japanese, 一晩中 (ひとばんじゅう) or 夜通し (よどおし) are more common.
It rained all night long.
Compound of 終 (end, throughout) and 宵 (early night, evening). The exact historical derivation is uncertain; it is a literary Sino-Japanese word.