A hyponym (in Greek: υπονύμιον, literally meaning 'few names') is a word whose extension is included within that of another word. For example, scarlet, vermilion, carmine and crimson are all hyponyms of red. A word is a unit of language that carries meaning and consists of one or more morphemes which are linked more or less tightly together. ...
According to Victoria Fromkin & Robert Rodman in their book "Introduction to Language" hyponyms are a set of related words whose meaning are specific instances of a more general word e.g., red, white, blue, etc., are hyponyms of the word color). Hyponymy is thus the relationship between a general term such as polygon and specific instances of it, such as the word triangle.
Examples: temperature-fever, drink-drink alcohol 1994 (MCMXCIV) was a common year starting on Saturday of the Gregorian calendar, and was designated the International year of the Family. ...
A hyponym is a word that is conceptually included within the definition of another word, as scarlet, vermilion, carmine and crimson are all hyponyms of red.
Tulip is a hyponym of flower, for instance, but not a synonym.
In his classic formulation, the linguist C.E. Bazell stated, "There is a relation of hyponymy when one word may invariable be replaced by a second word, but not vice-versa, without change of meaning."