Specialized reference works operate as catalysts and organizers of the terminological processes involved in the evolution of specialized concepts. This research aims to identify the term ‘knowl­edge organization system’ records and its synonymous or similar expressions in dictionaries, glossaries, vocabularies, and encyclopedias specialized in KO published over time. The research is qualitative and constitutes a study of punctual terminology, which introduces the perspective of dictionarization studies. The results yield fourteen terms representing more or less the same concept registered in the twelve reference works found. Among other conclusions, it is assumed that there has been progress towards terminological unification around the expression ‘knowl­edge organization system’.