Nagarjuna did not deny the existence of nibbana, but rather the fruitlessness of trying to describe it in words. This is because words are just complex schematics conditioned by greed, hatred, and delusion. Nibbana is unconditioned, and uncompounded. So to say it is a "thing", and a "word" is factual.
"One is not born a woman, but becomes one."- Simone de Beauvoir