A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in the same language. For example, the wordsbegin, start, commence, and initiate are all synonyms of one another; they are synonymous. The standard test for synonymy is substitution: one form can be replaced by another in a sentence without changing its meaning. Words are considered synonymous in one particular sense: for example, long and extended in the contextlong time or extended time are synonymous, but long cannot be used in the phrase extended family. Synonyms with exactly the same meaning share a seme or denotational sememe, whereas those with inexactly similar meanings share a broader denotational or connotational sememe and thus overlap within a semantic field. The former are sometimes called cognitive synonyms and the latter, near-synonyms, plesionyms or poecilonyms.
Lexicography
Some lexicographers claim that no synonyms have exactly the same meaning because etymology, orthography, phonic qualities, connotations, ambiguous meanings, usage, and so on make them unique. Different words that are similar in meaning usually differ for a reason: feline is more formal than cat; long and extended are only synonyms in one usage and not in others. Synonyms are also a source of euphemisms. Metonymy can sometimes be a form of synonymy: the White House is used as a synonym of the administration in referring to the U.S. executive branch under a specific president. Thus a metonym is a type of synonym, and the wordmetonym is a hyponym of the word synonym. The analysis of synonymy, polysemy, hyponymy, and hypernymy is inherent to taxonomy and ontology in the information-science senses of those terms. It has applications in pedagogy and machine learning, because they rely on word-sense disambiguation.
Synonyms often express a nuance of meaning or are used in different registers of speech or writing. Different technical fields may appropriate synonyms for specific technical meanings. Some writers avoid repeating the same word in close proximity, and prefer to use synonyms: this is called elegant variation. Many modern style guides criticize this.
Examples
Synonyms can be any part of speech, as long as both words belong to 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 with respect to certain senses of words: pupil as the aperture in the iris of the eye is not synonymous with student. Similarly, he expired means the same as he died, yet my passport has expired cannot be replaced by 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 because of its meta quality 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 are words that refer to, respectively, a general category and a specific instance of that category. For example, vehicle is a hypernym of car, and car is a hyponym of vehicle.
Homophones are words that have the same pronunciation, but different meanings. For example, witch and which are homophones in most accents.
Homographs are words that have the same spelling, but have different pronunciations. For example, one can record a song or keep a record of documents.
Homonyms are words that have the same pronunciation and spelling, but have different meanings. For example, rose and rose are homonyms.
