A false etymology (popular etymology, etymythology,  pseudo-etymology, or par(a)etymology), sometimes called folk etymology – although the last term is also a technical term in linguistics – is a popularly held but false belief about the origin or derivation of a specific word.
Such etymologies often have the feel of urban legends, and can be much more colorful and fanciful than the typical etymologies found in dictionaries, often involving stories of unusual practices in particular subcultures (e.g. Oxford students from non-noble families being supposedly forced to write sine nobilitate by their name, soon abbreviated to s.nob., hence the word snob).   Many recent examples are "backronyms" ( acronyms made up to explain a term), as in snob, and posh for "port outward, starboard homeward"; many other sourced examples are listed in the article on backronyms.
Erroneous etymologies can exist for many reasons. Some are reasonable interpretations of the evidence that happen to be false. For a given word there may often have been many serious attempts by scholars to propose etymologies based on the best information available at the time, and these can be later modified or rejected as linguistic scholarship advances. The results of medieval etymology, for example, were plausible given the insights available at the time, but have often been rejected by modern linguists. The etymologies of humanist scholars in the early modern period began to produce more reliable results, but many of their hypotheses have also been superseded.
Other false etymologies are the result of specious and untrustworthy claims made by individuals, such as the unfounded claims made by Daniel Cassidy that hundreds of common English words such as baloney, grumble, and bunkum derive from the Irish language.  
Some etymologies are part of urban legends, and seem to respond to a general taste for the surprising, counter-intuitive and even scandalous. One common example has to do with the phrase rule of thumb, meaning "a rough guideline". An urban legend has it that the phrase refers to an old English law under which a man could legally beat his wife with a stick no thicker than his thumb.  [a]
In the United States, some of these scandalous legends have had to do with racism and slavery; common words such as picnic,  buck,  and crowbar  have been alleged to stem from derogatory terms or racist practices. The "discovery" of these alleged etymologies is often believed by those who circulate them to draw attention to racist attitudes embedded in ordinary discourse. On one occasion, the use of the word niggardly led to the resignation of a US public official because it sounded similar to the unrelated word nigger. 
- "DOPE consists of etymological reanalysis of a pre-existent lexical item [...] The DOPE producer is applying his/her Apollonian Tendency, the wish to describe and create order, especially with unfamiliar information or new experience [...], the craving for meaningfulness."  DOPE is "merely passive", "mistaken derivation, where there is a rationalization ex postfacto." 
- GPE, on the other hand, involves the introduction of a new sense (meaning) or a new lexical item – see, for example, Phono-semantic matching.
- List of common false etymologies of English words
- Bongo-Bongo (linguistics)
- Chinese word for "crisis"
- Daniel Cassidy
- Etymological fallacy
- False cognate
- False friend
- Folk etymology
- Johannes Goropius Becanus
- Medieval etymology
- Phono-semantic matching
- Pseudoscientific language comparison
- Semantic change
- Slang dictionary
- Zuckermann, Ghil'ad (2003). Language Contact and Lexical Enrichment in Israeli Hebrew. Palgrave Macmillan. ISBN 978-1403917232.
- "nouns – Etymology of "snob" – English Language & Usage Stack Exchange". English.stackexchange.com. Retrieved 2013-08-26.
- "What is the origin of the word 'snob'? – Oxford Dictionaries Online". Oxforddictionaries.com. 2013-08-21. Retrieved 2013-08-26.
- Zwicky, Arnold (2007-11-09). "Language Log: Gullibility in high places". Itre.cis.upenn.edu. Retrieved 2015-07-12.
- Liberman, Mark (2006-07-06). "Language Log: The bunkum of "The Bunkum of Bunkum"?". Itre.cis.upenn.edu. Retrieved 2015-07-12.
- "World Wide Words: Rule of thumb". Quinion.com. 1999-11-13. Retrieved 2015-07-12.
- Mikkelson, David (21 January 2017). "Picnic Pique". Snopes.com. Retrieved 5 March 2018.
- "Etymology on the phrase 'passing the buck'". Snopes.com. Retrieved 2015-07-12.
- "Etymology of Crowbar". Snopes.com. Retrieved 2015-07-12.
- "Is "niggardly" a racist word?". The Straight Dope. 2000-01-03. Retrieved 2015-07-12.