Hypernymy and hyponymy

Hypernymy and hyponymy are the semantic relations between a generic term (hypernym) and a more specific term (hyponym). The hypernym is also called a supertype, umbrella term, or blanket term. The hyponym names a subtype of the hypernym. The semantic field of the hyponym is included within that of the hypernym. For example, "pigeon", "crow", and "hen" are all hyponyms of "bird" and "animal"; "bird" and "animal" are both hypernyms of "pigeon", "crow", and "hen".

In linguistics, semantics, general semantics, and ontologies, hyponymy (from Ancient Greek ὑπό (hupó) 'under' and ὄνυμα (ónuma) 'name') 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.

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 as most immediately understood refers to the screwdriver tool, and not to the screwdriver drink.

Hypernymy and hyponymy are converse relations. If X is a kind of Y, then X is a hyponym of Y and Y is a hypernym of X. 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 seen in hyponymy. These can be conceptualized as a vertical arrangement, 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.

Taxonymy (not to be confused with, though related to, taxonomy) is a sub-variety of hyponymy. Within the structure of a taxonomic lexical hierarchy, two types of hyponymic relation may be distinguished: the first—exemplified in "An X is a Y"—corresponds to so-called "simple" hyponymy; the second—that which is exemplified in "An X is a kind/type of Y"—is more discriminating, and functions as the "vertical" relation in the taxonomy. This latter relation is that which may be termed taxonymy.

(Note that a taxonomic lexical hierarchy is structured by, in addition to the above inclusion relations, their corresponding relations of exclusion: "A Z is not a Y", or incompatibility; and "A Z is a different kind/type of Y than X", or co-taxonymy.)

If the hypernym Z consists of hyponyms X and Y, then X and Y are identified as co-hyponyms, 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.