What does Nishka mean?
From the Sanskrit निष्क (niṣka), an ancient gold coin, and by extension a golden necklace or ornament — attested in the Manusmriti and other classical texts. Popular 'pure/honest' glosses on name sites are not supported by the classical sources.
What does Nitya mean?
From Sanskrit nitya (नित्य), 'eternal, perpetual, constant'; also used as an epithet of the Goddess (Durga/Devi). Well established.