>I turned it into a noun
Just because I am a grammarfag (but not grammarnazi), Svengali (with a capital) is already a noun, a proper noun. If you want it to be describtive (sic) it then becomes an adjective as an adjective describes a noun in the same way that an adverb describes a verb.
Interestingly, the word for noun in Latin languages is the same as the word for name because that is exactly what a noun is - the name of someone or something.
(ETA, what a beautifully clear captcha today)