"improbation" means: The act by which falsehood and forgery are proved; an action brought for the purpose of having some instrument declared false or forged.. This is technical or formal vocabulary, more likely to appear in school work, news or a particular profession than in peer chat. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your child uses the term, it is usually a sign of curiosity about a subject area. A short follow-up question about where they came across it is usually all that is needed.