hyponymy

Hyponymy is a semantic relation between lexical items in which the sense of one word, called the hyponym, is included in the sense of another word, the hypernym. The hyponym denotes a subset of the class denoted by the hypernym; every instance of the hyponym is an instance of the hypernym. For example, dog is a hyponym of animal; robin is a hyponym of bird; car is a hyponym of vehicle. Conversely, bird is a hypernym of robin and animal is a hypernym of dog. The relation is often expressed through the neutral form “is a” as in “a robin is a bird.” It is a fundamental part of lexical hierarchies in many languages and dictionaries.

Properties of hyponymy include its transitivity: if a is a hyponym of b and b is a hyponym of c, then a is a hyponym of c. It is antisymmetric: if a is a hyponym of b and b is a hyponym of a, then a and b refer to the same concept. It is not symmetric; a hypernym is not a hyponym of its own.

Applications of hyponymy are prominent in lexical databases such as WordNet, where terms are organized into taxonomies through hyponym-hypernym links. It supports tasks in natural language processing such as word sense disambiguation, information retrieval, entailment recognition, and semantic similarity assessment. Hyponymy is distinct from meronymy (part-whole relationships) and from synonymy (alternate forms of the same sense); it concerns kind-category relationships rather than parts or sameness.