Is this a glossary, a lexicon, or a thesaurus? How to tell them apart.

The Semantic Ladder

We have all come up with different types of controlled vocabularies and the truth is sometimes we don’t know if we are dealing with a glossary, a thesaurus, or a lexicon because in real life they tend of be used interchangeably, even in other languages. The French Wikipedia says that “Le terme glossaire est souvent confondu avec lexique”, and the “Financial Times Lexicon”, says in its introduction that you may “suggest new terms for this glossary”.

In my recent post on Realiter glossaries, most lexicons in the cover pages were translated into English as “glossaries” not lexicons. Some of them had definitions; some of them only included terms. So, how to know if we are using the right term? Indeed, it’s not an easy task, but I have gathered some definitions that I think will help us get a more clear differentiation. Do you have better definitions? Feel free to share them!



Preferred definition Source
Glossary Alphabetical list of terms in a particular domain of knowledge with the definitions for those terms. TermTerm
Specialized vocabulary with definitions but does not provide other information about the words.
Terminological dictionary which contains a list of designations from a subject field, together with equivalents in one or more languages. NOTE: In English common language usage, glossary can refer to a unilingual list of designations and definitions in a particular subject field. IATE(ISO 1087:2000)
A stock of terms used in a particular profession, subject, or style; a vocabulary. The Free Dictionary.Merriam Webster also uses them as synonyms. So technically a lexicon should not be a glossary.
Nomenclature A system of generating new terms for a particular field. Nomenclature is a set of external rules. A good nomenclature system has few rules all of which should be understood and applied, preferably with reproducible results, by more than one person. A blogpost by Metallone explains the difficulties in differentiating it from terminology and proposes working definitions for each. (Recommended).
Ontology Ontology, like a thesaurus, is a kind of taxonomy with structure and specific types of relationships between terms… relationships are greater in number and more specific in their function. They are used in more complex information systems, such as the Semantic Web. Taxonomies
Taxonomy A simple hierarchical arrangement of entities where you have a parent-child kind of relationship. Dimitrov, Marin What’s the difference between ontology and taxonomy? (Quora)
Taxonomy is the simplest variant [of controlled vocabularies] as it contains only terms that are organized into a hierarchical structure. Grips Semantic Web
Taxonomy versus ontology On the technical side, ontologies imply a broader scope of information. People often refer to a taxonomy as a ‘tree’, and extending that analogy I’d say that an Ontology is often more of a “forest”. An ontology might encompass a number of taxonomies, with each taxonomy organizing a subject in a particular way New Idea Engineering
Terminology Set of designations belonging to one special language ISO 1087-1:2000
Thesaurus Is a taxomony that includes related and synonymous terms/words, or “associative relationships as explained in The Accidental Taxonomist in a blog post they published on this topic. They go on to say that “This is largely true, and I will add that a thesaurus also must have equivalence relationships (between a “preferred term” and its synonyms or nonpreferred terms), whereas synonyms/nonpreferred terms are merely optional in taxonomies, depending on the taxonomy size
Topic map A standard for the representation and interchange of knowledge, with an emphasis on the findability of information. Similar to concept maps and mind maps in many respects, though only Topic Maps are ISO standards. Topic Maps are a form of semantic web technology similar to RDF (Resource Description Framework)


5 Comments on “Is this a glossary, a lexicon, or a thesaurus? How to tell them apart.

  1. Very interesting issue and often confusing as well! May I add some thoughts?
    I would say that all these are knowledge organization methods (and tools), contributing, more or less, to semantic representation and management of knowledge in general. Especially for the thesaurus, its characteristic is that it is a concept-centric controlled vocabulary based on relationships between concepts (not terms). I would say it is not (just or at all in some cases) a glossary. it is more than a taxonomy and less than an ontology (although I think that ontologies development may eliminate the need for thesauri development, in the near future perhaps).
    May I add the ISO 25964 definition for thesaurus: “controlled and structured vocabulary in which concepts are represented by terms, organized so that relationships between concepts are made explicit, and preferred terms are accompanied by lead-in entries for synonyms or quasi-synonyms”.
    Friendly, Katerina.

  2. Wow. Excellent comment Katerina. Thanks for sharing such useful information and hopefully trigger some more comments. Really appreciated.

  3. Thanks. Was just wondering what to title my recently compilation of definitions of commonly used +7,000 words of General Insurance, Reinsurance and Risk Management. With your help I have now titled it as “General Insurance, Reinsurance and Risk Management Glossary”. Thanks a million for providing clarity at the right time and need.

  4. I´m glad that my blog post was helpful. Thanks for the feedback.

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