adverb
all night; throughout the night
Poetic or literary adverb meaning 'all night long'; often used in classical or elevated contexts. In modern Japanese, 一晩中 (ひとばんじゅう) is more common in everyday speech.
夜もすがら月を眺めていた。
I gazed at the moon all night long.
夜もすがら降り続いた雨が、朝には上がっていた。
The rain that fell throughout the night had stopped by morning.
From classical Japanese; 夜 (yo, 'night') + も (mo, 'even') + すがら (sugara, 'throughout'). The suffix すがら is an old form meaning 'all through' or 'during', related to ながら (nagara).