Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time. By an extension, the term "etymology (of a word)" means the origin of a particular word.

For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during earlier periods of their history and when they entered the languages in question. Etymologists also apply the methods of comparative linguistics to reconstruct information about languages that are too old for any direct information to be available. By analyzing related languages with a technique known as the comparative method, linguists can make inferences about their shared parent language and its vocabulary. In this way, word roots have been found that can be traced all the way back to the origin of, for instance, the Indo-European language family.

Even though etymological research originally grew from the philological tradition, currently much etymological research is done on language families where little or no early documentation is available, such as Uralic and Austronesian.

The word asshole, a variant of arsehole, which is still prevalent in British and Australian English, is a vulgar to describe the anus, often pejoratively used to refer to people.

The word arse in English derives from the Germanic root *arsaz, which originated from the Proto-Indo-European root *ors — meaning buttocks or backside. The combined form arsehole is first attested from 1500 in its literal use to refer to the anus. The metaphorical use of the word to refer to the worst place in a region, e.g., "the arsehole of the world") is first attested in print in 1865; the use to refer to a contemptible person is first attested in 1933. In the ninth chapter of his 1945 autobiography, Black Boy, Richard Wright quotes a snippet of verse that uses the term: "All these white folks dressed so fine / Their ass-holes smell just like mine ...". Its first appearance as an insult term in a newspaper indexed by Google News is in 1965. As with other vulgarities, these uses of the word may have been common in oral speech for some time before their first print appearances. By the 1970s, Hustler magazine featured people they did not like as "Asshole of the Month." In 1972, Jonathan Richman's Modern Lovers recorded his song "Pablo Picasso," which includes the line "Pablo Picasso was never called an asshole."