In linguistics, word formation is the creation of a new word. Word formation is sometimes contrasted with semantic change, which is a change in a single word's meaning. The boundary between word formation and semantic change can be difficult to define: a new use of an old word can be seen as a new word derived from an old one and identical to it in form (see conversion). Word formation can also be contrasted with the formation of idiomatic expressions, although words can be formed from multi-word phrases (see compound and incorporation).
Types of word formation 
There are a number of methods of word formation.
Morphological word formation 
There are three subcategories; words created by derivation, words created by compounding, and words created by back-formation.
Derivation is the process of forming new words from existing ones by adding affixes to them, like shame + less + ness → shamelessness. In cases in which there is a one-to-one correspondence between affixes and syntactical categories, this is known as agglutination, as seen in agglutinative languages.
A compound is a word formed by stringing together older words, like the formation of earthquake from earth and quake.
A sub-category of compounding is incorporation, which is a compound of a verb and an object or particle, like intake, a compound of the verb take with the preposition in.
Back-formation is word-formation via removing seeming affixes from existing words, such as forming edit from editor.
A blend is a word formed by joining parts of two or more older words. An example is smog, which comes from smoke and fog.
Sub-categories of blending are:
- Acronym (a word formed from initial letters of the words in a phrase, like English laser from light amplified by stimulated emission of radiation)
- Clipping (morphology) (taking part of an existing word, like forming ad from advertisement)
A Calque is a word or phrase borrowed from another language by literal, word-for-word or root-for-root translation; for example the English phrase to lose face is a calque from Chinese
A sub-category of Calquing is the semantic loan, that is, the extension of the meaning of a word to include new, foreign meanings.
Conversion involves forming a new word from an existing identical one, like forming the verb green from the existing adjective.
A neologism is a completely new word, like quark.
Subcategories of neologisms include:
- The eponym, a proper noun that becomes commonly used for an idea it is associated with, usually by changing its part of speech, like Xerox, Orwellian, and Stentorian
- The loanword, a word borrowed from another language, as cliché is from French
- An onomatopoeic word, a word which imitates natural sounds, like the bird name cuckoo
- Formation using Phono-semantic matching, that is, matching a foreign word with a phonetically and semantically similar pre-existent native word/root
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- Joachim Grzega (2004), Bezeichnungswandel: Wie, Warum, Wozu? Ein Beitrag zur englischen und allgemeinen Onomasiologie, Heidelberg: Winter.
- Peter Koch (2002), “Lexical Typology from a Cognitive and Linguistic Point of View”, in D. Alan Cruse et al. (eds), Lexicology: An International Handbook on the Nature and Structure of Words and Vocabularies / Lexikologie: Ein internationales Handbuch zur Natur und Struktur von Wörtern und Wortschätzen, [Handbücher zur Sprach- und Kommunikationswissenschaft 21], Berlin/New York: Walter de Gruyter, vol. 1, pp. 1142-1178.
- Ghil'ad Zuckermann (2003). Language Contact and Lexical Enrichment in Israeli Hebrew. Houndmills: Palgrave Macmillan. (Palgrave Studies in Language History and Language Change). ISBN 1-4039-1723-X.