adverb
all night; throughout the night
Poetic or literary adverb meaning 'all night long'. Often used in classical or elevated contexts. Compare with 夜もすがら, which has the same meaning.
See also: 夜もすがら
夜すがら月を眺めて過ごした。
I spent the whole night gazing at the moon.
夜すがら降り続いた雨が朝には上がって
The rain that fell all night had stopped by morning.
Synonymous; 夜もすがら is slightly more emphatic with the particle も, but both mean 'all night' and are used in similar literary contexts.
Same kanji spelling but different reading and usage; しゅうや is a more common Sino-Japanese word meaning 'all night', used in compounds like 終夜運転 (all-night service).
Compound of 夜 (yo, 'night') + すがら (sugara, 'throughout, all along'). The suffix すがら is an archaic element meaning 'while, during, throughout', also seen in words like 道すがら (all along the way).