Synonym

Some lexicographers argue that no synonyms are identical (in all contexts or social levels of language) due to differences in etymology, orthography, phonic qualities, connotations, ambiguous meanings, and usage. For example, feline is more formal than cat, and a long arm is not the same as an extended arm, as long and extended are not always interchangeable. Synonyms can also be used as euphemisms.

Metonymy is sometimes a type of synonymy. For example, White House is often used as a synonym of the administration to refer to the U.S. executive branch under a specific president. In this context, metonymy functions as a hyponym of synonymy.

The study of synonymy, polysemy, hyponymy, and hypernymy is essential in information science for taxonomy and ontology. This analysis is also important in pedagogy and machine learning for word-sense disambiguation.

The term synonym is derived from the Latin word synōnymum, which was borrowed from the Ancient Greek word synōnymon (συνώνυμον). It is composed of the Greek elements sýn (σύν, meaning 'together, similar, alike') and -ōnym- (-ωνυμ-), a form of onoma (ὄνομα, meaning 'name').

Synonyms often convey subtle differences in meaning or are employed in various speech or writing registers.

Different technical fields may use synonyms to express specific technical distinctions.

Elegant variation is the practice of using synonyms to avoid repetition of the same word in proximity by using synonyms. However, modern style guides often criticize this practice.

Synonyms can be any part of speech, as long as both words are of the same part of speech. Examples:

• noun: drink and beverage
• verb: buy and purchase
• adjective: big and large
• adverb: quickly and speedily
• preposition: on and upon

Synonyms are defined according to certain senses of words. For example, pupil refers to the aperture in the eye, not a student. He expired is synonymous with he died, but my passport has expired cannot be replaced with my passport has died.

A thesaurus or synonym dictionary lists similar or related words; these are often, but not always, synonyms.

• The word poecilonym is a rare synonym of the word synonym. It is not entered in most major dictionaries and is a curiosity or piece of trivia for being an autological word due to its meta nature as a synonym of synonym.
• Antonyms are words with opposite or nearly opposite meanings. For example, hot ↔ cold, large ↔ small, thick ↔ thin, synonym ↔ antonym
• Hypernyms and hyponyms represent a broader category and a specific instance within that category. For instance, vehicle is a hypernym of car, while car is a hyponym of vehicle.
• Homophones are words that sound the same but have different meanings. For example, witch and which are homophones in most accents because they are pronounced in the same way.
• Homographs are words that are spelled the same but have different meanings. For example, record can refer to both the act of recording a song and keeping a record of documents.
• Homonyms are words that have the same pronunciation and spelling but different meanings. For example, rose can refer to a type of flower or the past tense of rise.