"legitness" means: Legitness is the noun form of 'legit' — it captures the degree to which something or someone is authentic, credible, or genuinely impressive.... This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.