counter for nights
「夜」 has another reading with different meanings.
night; evening
二夜続けて雨が降った。
It rained for two nights in a row.
三夜も寝られなくて辛かったです。
Not sleeping for three nights was tough.
一夜で雪がたくさん積もりましたね。
A lot of snow piled up in just one night.