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1.
Nasti is when something is gross, or nasty, but when you add the "i" at the end, it becomes slutty-ier.
Bob: "That girl Candi is sooo nasti"
Jimmy: "True dat brotha, nasti!"
by Jeff Aschkin April 24, 2008
 
2.
Acronym for National Strategy for Trusted Identities. Pronounced the same as "nasty".
Some people have started referring to the proposed "National Strategy for Trusted Identities" as NaSTI, as both a time saver and as an opinion.
by empathy4uTM January 11, 2011