night vs wedding night

night and wedding night both are nouns.

Word	Noun	Adjective	Verb	Adverb
night	Yes	No	No	No
wedding night	Yes	No	No	No

As nouns, wedding night is a hyponym of night; that is, wedding night is a word with a more specific, narrower meaning than night:

night: the time after sunset and before sunrise while it is dark outside
wedding night: the night after the wedding when bride and groom sleep together

Other hyponyms of night include weeknight.

night (noun)	wedding night (noun)
darkness	the night after the wedding when bride and groom sleep together
the time after sunset and before sunrise while it is dark outside
a period of ignorance or backwardness or gloom
the dark part of the diurnal cycle considered a time unit
the time between sunset and midnight
the period spent sleeping
a shortening of nightfall