"Variant of Anastasia"
The name Nastassia is commonly a female name from the "Russian" origin.
Nastassia is a variant spelling of Anastasia, the feminine form of the Greek name Anastasios, which derives from anastasis, meaning resurrection. It corresponds to the Russian familiar form Nastasya and to the German-written Nastassja, and it keeps the meaning of the name it varies rather than carrying one of its own.
Anastasia means "Resurrection; springtime".
The pronunciation of Nastassia is nah-STAH-shuh.