Retronym
WordNet
noun
(1) A word introduced because an existing term has become inadequate
"Nobody ever heard of analog clocks until digital clocks became common, so `analog clock' is a retronym"
WiktionaryText
Etymology
- retr(o)- + -onym; coined by Frank Mankiewicz and popularized by William Safire http://www.startribune.com/stories/389/4224163.html in The New York Times
Noun
- 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).