Definition
Theres a different between Dhahir and nass. The mujtahid would use the support of a daleel to ascertain the dhahir meaning.
Nass is when it is dhahir, but it requires a bit of justification using daleel.
Dhahir does not require the intention of the speaker, but nass requires some information about the intention.
Example
The ayah for marrying multiple, it makes permissible marrying multiple, the nass principle applied is that there is a limit that Allah has set for the number of women you can marry.
The dhahir meaning is marry more than one The nass meaning is marry maximum 4
