In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889. (OED online first definition of 'back formation' is from the definition of to burgle, which was first published in 1889.)
Back-formation is different from clipping – back-formation may change the part of speech or the word's meaning, whereas clipping creates shortened words from longer words, but does not change the part of speech or the meaning of the word.
For example, the noun resurrection was borrowed from Latin, and the verb resurrect was then backformed hundreds of years later from it by removing the ion suffix. This segmentation of resurrection into resurrect + ion was possible because English had examples of Latinate words in the form of verb and verb+-ion pairs, such as opine/opinion. These became the pattern for many more such pairs, where a verb derived from a Latin supine stem and a noun ending in ion entered the language together, such as insert/insertion, project/projection, etc.
Back-formation may be similar to the reanalyses of folk etymologies when it rests on an erroneous understanding of the morphology of the longer word. For example, the singular noun asset is a back-formation from the plural assets. However, assets is originally not a plural; it is a loan-word from Anglo-Norman asetz (modern French assez). The -s was reanalyzed as a plural suffix.
Back-formation in the English language 
Many words came into English by this route: Pease was once a mass noun but was reinterpreted as a plural, leading to the back-formation pea. The noun statistic was likewise a back-formation from the field of study statistics. In Britain, the verb burgle came into use in the 19th century as a back-formation from burglar (which can be compared to the North American verb burglarize formed by suffixation).
Other examples are:
- Adjective "couth" from "uncouth"
- Noun Taxon a unit of classification in Taxonomy, derived from Greek (language) taxis (arrangement)+nomia "distribution"
- Singular "sastruga", plural "sastrugi" (from Russian): new Latin-type singular "sastrugus" has been used sometimes
- Singular "syringe", from plural "syringes"; the original Greek singular form is syrinx
- Verb "edit" from "editor"
- Verbs "euthanase" or "euthanize" from the noun "euthanasia".
Even though many English words are formed this way, new coinages may sound strange, and are often used for humorous effect. For example, gruntled (from disgruntled) would be considered a barbarism, and used only in humorous contexts, such as by P.G. Wodehouse, who wrote "He spoke with a certain what-is-it in his voice, and I could see that, if not actually disgruntled, he was far from being gruntled". The comedian George Gobel regularly used original back-formations in his humorous monologues. Bill Bryson mused that the English language would be richer if we could call a tidy-haired person shevelled – as an opposite to dishevelled. In the American sitcom Scrubs, the character Turk once said when replying to Dr. Cox, "I don't disdain you! It's quite the opposite – I dain you." However, though the foregoing examples illustrate a process of intentional back-formation, they illustrate the difficulty of avoiding collisions in definition when coining words by such processes. Gruntle and dain both are long-established words, and prefixing them with dis- does not invert the meaning of either; gruntle actually is the etymological source of the formation of disgruntle, but it means to make a grunting noise, generally in the sense of complaining. Dain is simply a dialect contraction of disdain, without any difference in meaning, and in spite of claims to the contrary, neither dain nor deign was derived from the other.
Back-formations frequently begin in colloquial use and only gradually become accepted. For example, enthuse (from enthusiasm) is gaining popularity, though it is still considered substandard by some today.
The immense celebrations in Britain at the news of the relief of the Siege of Mafeking briefly created the verb to maffick, meaning to celebrate both extravagantly and publicly. "Maffick" is a back-formation from Mafeking, a place-name that was treated humorously as a gerund or participle. There are many other examples of back-formations in the English language.
See also 
- List of English back-formations
- Folk etymology
- Juncture loss
- Unpaired word
- Crystal, David. A Dictionary of Linguistics and Phonetics, Sixth Edition, Blackwell Publishers, 2008.
- The Funny Side of English, by O.A. Booty, p. 29
- Bryson, Bill (1990). The Mother Tongue. HarperCollins.
- Brown, Lesley (1993). The New shorter Oxford English dictionary on historical principles. Oxford [Eng.]: Clarendon. ISBN 0-19-861271-0.