The word retronym also refers to an acronym constructed after the fact (a backronym), such as Perl. It is also used to refer to a word formed by reversing the spelling of another word, e.g., mho from ohm.
In 2000, The American Heritage Dictionary (4th edition) became the first major dictionary to include the word retronym.
Examples of retronyms are "acoustic guitar" (coined when electric guitars appeared), World War I (called "the Great War" or "the World War" until World War II) and analog watch to distinguish from a digital watch.
It is not always obvious which is the retronym and which is the non-retronym. "Leaded gasoline" (petrol) could be considered the retronym since that term was used after the introduction of unleaded gasoline. However, lead is actually an additive that was not originally in gasoline.
Posthumous names awarded in East Asian cultures to royalty after their death can be considered retronyms too, although their birth names will remain unambiguous.
Careless use of retronyms in historical fiction can cause anachronisms. For example, referring to the "First World War" in a piece set in 1935 would be incorrect — "The Great War" and "14-18 War" were commonly employed descriptions. Anachronistic use of a retronym could also betray a modern document forgery (such as a description of the First Battle of Bull Run before the second had taken place).
In the early 2000s, liquid dish detergent became available as a concentrate, allowing a bottle of the same size to be used to wash more (or dirtier) dishes. The common nomenclature for such products was "ultra" strength (e.g., Ultra-Dawn). Some consumers prefer the original (and generally cheaper) formulas, which in some cases are still available in a re-labeled "non-ultra" form.
The advent of digital telephony services such as ISDN led to analog services being described as "plain old telephone service" (or simply POTS), primarily within the telephone industry. As mobile telephones have become prevalent, many consumers have come to refer to POTS service as "land line" phone service – although calls placed on such a line may traverse wireless links such as microwave and satellite.
During the late 19th and early 20th centuries, Mexico was sometimes referred to (particularly in the U.S.) as "Old Mexico", to differentiate it from the territory and later state of New Mexico. "Old Mexico" is an example of a retronym that gradually fell into disuse, and is rarely heard today outside of Westerns.
Simón Bolívar united Venezuela, New Granada, and Ecuador under the name Colombia. After the union was later dissolved, New Granada changed its name to Colombia. Historians coined the term Gran Colombia (Great Colombia) to refer to Bolivar's union.
One example is the original 1960s Star Trek television series, which is now referred to as Star Trek: The Original Series (or ST:TOS) to distinguish it from the many film and television sequels that Star Trek has spawned.
Another is the first Star Wars movie to be filmed and released, originally titled simply Star Wars; after the film became a success and sequels were assured, the film was subtitled Episode IV: A New Hope for all subsequent releases.
"Classic" is often applied to the first computer game in a franchise, especially if the sequels are numerically titled; examples include the Doom, Quake, and Unreal Tournament series. (Doom and Doom II are often collectively referred to as Classic Doom to distinguish them from Doom 3, which uses a different game engine.)
CSI: Crime Scene Investigation, which is set in Las Vegas, Nevada, has spawned two spin-off series, CSI: Miami and CSI: New York. The original series' title has not changed, but it is syndicated in some markets with the new title CSI: Las Vegas.