A word or phrase created because an existing term that was once used alone needs to be distinguished from a term referring to a new development, as acoustic guitar in contrast to electric guitar or analog watch in contrast to digital watch.
Retronym. (n.d.). In YourDictionary. Retrieved from https://www.yourdictionary.com/Retronym
A new word or phrase coined for an old object or concept whose original name has become used for something else or is no longer unique (such as acoustic guitar where guitar used to mean this but can now also refer to an electric guitar).
retro- +"Ž -onym; coined by Frank Mankiewicz and popularized by William Safire in The New York Times
English Wiktionary. Available under CC-BY-SA license.