night has 3 distinct synonyms spread across 2 of its 8 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is day.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the time after sunset and before sunrise while it is dark outside
a period of ignorance or backwardness or gloom
the period spent sleeping
“I had a restless night”
the dark part of the diurnal cycle considered a time unit
“three nights later he collapsed”
a shortening of nightfall
“they worked from morning to night”
the time between sunset and midnight
“he watched television every night”
Roman goddess of night; daughter of Erebus; counterpart of Greek Nyx
Synonyms, antonyms and the broader and narrower relations for night come from Princeton University’s WordNet. Full sources and licences.