"preclare" means: Preclare is an obsolete Scots and literary adjective meaning illustrious, distinguished, or eminent — of great renown. Derived from the Lati.... 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.