An interactive version of IUPAC Compendium of Chemical Terminology, also knows as the "Gold Book". It contains extensive chemical terminology with definitions, synonyms, acronyms, and abbreviations (more than 6400 terms in April 2024).
You can search names of chemical compounds and radicals by formulas in the sections "Generalized Chemical Formulae" & "Exact Chemical Formulae" & Ring Index and use other indexes, in additional to the classic alphabetical one.
The Compendium is supported by International Union of Pure and Applied Chemistry.