(dated, originally) The night before May Day. / (UK) The night before Bonfire Night.

(around New York City) A particular night, commonly the night of 30 or 31 October, during which young people play pranks and do mischief in their neighborhoods.

During the night before last night; two nights ago.

(emergency medicine) Initialism of biological, nuclear / radiological, incendiary, chemical, and explosive agents, used to remember the types of hazmat emergencies.

(simile) Perfectly all right; fine. / (simile) Neat, tidy, in order.

The official name of Niger.

The official name of Nigeria.

(archaic) The lamprey.

plural of nicker tree

(botany) The plant (genus Caesalpinia) producing nicker nuts.