The word nirvāṇa is irregularly formed by changing the niṣṭhā ta is changed to na when the sense is not that of 'wind'.,
The word निर्वाण is formed from the root वा, with the preposition निर् and the Participial affix त ॥ Thus निर्वाणोऽग्निः = उपशान्तः, निर्वाणः प्रदीपः, निर्वाणो भिक्षुः = उपरतः ॥
Why do we say when not meaning \the wind\? Observe, निर्वातो वातः, निर्वातं वातेन ॥
In the sentences निर्वाणः प्रदीपो वातेन, निर्वाणोऽग्निर्वातेन, the न change has taken place, because the location of the verb वा is in the प्रदीप and अग्नि, and not in the वात, which is merely an Instrument. Hence the above vritti uses the words \if the sense of the verb वा does not govern वात in the locative case\.,