What does Gauri mean?
From the Sanskrit गौरी (gaurī), 'fair, white, brilliant'. It is a classic epithet of the goddess Parvati, consort of Shiva, in her radiant form.
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.