Hyponymy and hypernymy are semantic relations between a term belonging in a set that is defined by another term and the latter. In other words, the relationship of a subtype (hyponym) and the supertype (also called umbrella term, blanket term, or hypernym). The semantic field of the hyponym is included within that of the hypernym. For example, pigeon, crow, and eagle are all hyponyms of bird, their hypernym.
Hyponyms and hypernyms
In linguistics, semantics, general semantics, and ontologies, hyponymy () shows the relationship between a generic term (hypernym) and a specific instance of it (hyponym). A hyponym is a word or phrase whose semantic field is more specific than its hypernym. The semantic field of a hypernym, also known as a superordinate, is broader than that of a hyponym. An approach to the relationship between hyponyms and hypernyms is to view a hypernym as consisting of hyponyms. This, however, becomes more difficult with abstract words such as imagine, understand and knowledge. While hyponyms are typically used to refer to nouns, it can also be used on other parts of speech. Like nouns, hypernyms in verbs are words that refer to a broad category of actions. For example, verbs such as stare, gaze, view and peer can also be considered hyponyms of the verb look, which is their hypernym.
Hypernyms and hyponyms are asymmetric. Hyponymy can be tested by substituting X and Y in the sentence "X is a kind of Y" and determining if it makes sense. For example, "A screwdriver is a kind of tool" makes sense, but not "A tool is a kind of screwdriver".
Strictly speaking, the meaning relation between hyponyms and hypernyms applies to lexical items of the same word class (that is, part of speech), and holds between senses rather than words. For instance, the word screwdriver used in the previous example refers to the screwdriver tool, and not to the screwdriver drink.
Hyponymy is a transitive relation: if X is a hyponym of Y, and Y is a hyponym of Z, then X is a hyponym of Z. For example, violet is a hyponym of purple and purple is a hyponym of color; therefore violet is a hyponym of color. A word can be both a hypernym and a hyponym: for example purple is a hyponym of color but itself is a hypernym of the broad spectrum of shades of purple between the range of crimson and violet.
The hierarchical structure of semantic fields can be mostly seen in hyponymy. They could be observed from top to bottom, where the higher level is more general and the lower level is more specific. For example, living things will be the highest level followed by plants and animals, and the lowest level may comprise dog, cat and wolf.
Under the relations of hyponymy and incompatibility, taxonomic hierarchical structures too can be formed. It consists of two relations; the first one being exemplified in "An X is a Y" (simple hyponymy) while the second relation is "An X is a kind/type of Y". The second relation is said to be more discriminating and can be classified more specifically under the concept of taxonomy.
Co-hyponyms
If the hypernym Z consists of hyponyms X and Y, then X and Y are identified as co-hyponyms (cohyponyms), also known as coordinate terms. Co-hyponyms are labelled as such when separate hyponyms share the same hypernym but are not hyponyms of one another, unless they happen to be synonymous. For example, screwdriver, scissors, knife, and hammer are all co-hyponyms of one another and hyponyms of tool, but not hyponyms of one another: *"A hammer is a type of knife" is false.
Co-hyponyms are often but not always related to one another by the relation of incompatibility. For example, apple, peach and plum are co-hyponyms of fruit. However, an apple is not a peach, which is also not a plum. Thus, they are incompatible. Nevertheless, co-hyponyms are not necessarily incompatible in all senses. A queen and mother are both hyponyms of woman but there is nothing preventing the queen from being a mother. This shows that compatibility may be relevant.