A city begins using “extreme heat” as an administrative category. The term enters risk maps, emergency protocols, budgets and building guidance. It is no longer only a weather description. Remove the term and several procedures lose their justification. This is SemanticHardening because the cost of revision has become institutional. It is not RecurrenceMass alone: repetition matters, but dependency is the decisive mechanism. Test it by removing the term from the planning framework and listing every map, threshold, budget line and emergency action that must be rewritten. SemanticHardening: https://socioplastics.blogspot.com/2026/05/socioplastics-503-semantic-hardening.html DOI: https://doi.org/10.5281/zenodo.18680418