Hyponymy and hypernymy

In linguistics, a hyponym is a word that can be changed with a different and less precise word without changing the overall meaning of the phrase. The different word is its hyperonym, hypernym or superordinate term. Hyponymy is a relation to a more generic word. A hyponym can be part of a group of words on a similar level that can all be replaced by the same hypernym. For example, "pigeon", "crow", "eagle" and "seagull" are all hyponyms (co-hyponyms) of "bird" (their hypernym). In turn, bird is a hyponym of "animal". In a sentence such as 'The pigeon is flying over the church.', it is possible to change the word pigeon to "bird" or "animal" without changing the overall meaning of the sentence. This is because "pigeon" is a hyponym of both "bird" and "animal". 
A hypernym is sometimes also called an umbrella term or a blanket term. 
The word Hyponym comes from the Greek "hupó", "under" and "ónoma", "name". Hypernym comes from the Greek "hupér", "over" and "ónoma", "name". A hyponym can also sometimes be a phrase. A word can be both a hypernym and a hyponym.
Usage.
In Computer science this relationship is often called an "is-a" relationship. For example, the phrase 'Red is-a colour' describes the hyponymic relationship between "red" and "colour".
The idea of hyponymy is very important in language translation. This is because hyponyms are very common across languages. For example, in Japanese the word for 'older brother' is , and the word for 'younger brother' is . An English-to-Japanese translator needs to choose which Japanese word to use to translate the English word "brother". This can be difficult during machine translation because this information is often not available.