Names and descriptions
Naming and describingDefinitions play a primary role. You can add nuance to the descriptions: examplesmultiple definitions, quotes, pronunciations, dictionaries from different sources, and more.
Naming and describing play a minor role. You can add a simple description and alternate names, but no advanced features exist.
Hierarchies (also known as trees or ontologies) play a very minor role. While very simple hierarchical structures are possible, you can't create very sophisticated relationships between terms.
In subjects, ontologies play a primary role. You can create complex relationships between subjects.