also: そや
noun
wedding night; first night of marriage
Refers to the first night after a wedding ceremony; somewhat formal or literary.
二人は初夜を静かに過ごした。
The two spent their wedding night quietly.
noun
first watch of the night
Historical term for the first division of the night in the old timekeeping system; rarely used in modern contexts.
昔の時刻では、初夜は戌の刻にあたる。
In the old time system, the first watch of the night corresponds to the hour of the dog.
Compound of 初 (first) and 夜 (night). The reading しょや is the standard on'yomi combination; そや is an older or alternative reading.