noun, adverb
every night; nightly
Indicates that something happens each night, often as a regular occurrence. Can be used as a noun or adverbially.
夜ごと星を眺めるのが日課だ。
Looking at the stars every night is my daily routine.
彼は夜ごと遅くまで働いている。
He works late every night.
毎晩 is the most common and neutral way to say 'every night'. 夜ごと is slightly more literary or emphatic, often implying a repeated nightly event.
夜な夜な is an adverb meaning 'night after night', often with a nuance of something happening habitually or secretly. 夜ごと is more straightforward and can be used as a noun.
Compound of 夜 (yo, 'night') and the suffix ごと (goto, 'every'). The suffix ごと attaches to nouns to mean 'each' or 'every'.