An ELT Glossary : Hyponymy

• Definition : A lexical relationship in which one word describes a category and other words the members of that category.

• Examples :  

          vehicle / car, bus, truck, etc

          mammal / horse, dog, rabbit etc

          fruit / apple, peach / orange etc

• The word describing the category (the first word in the examples) is known as the superordinate; the members of the category are called co-hyponyms.

Further Reading 

Gairns and Redman, Working with Words, Cambridge