A RetroNym is a new word or phrase coined for an old object or concept whose original name became used for something else. "Retronym" is a neologism coined by Frank Mankiewicz and popularized by William Safire in 1980 in the New York Times. A lot of these are created by advances in technology -- examples include "snail mail", "natural language", "acoustic guitar", etc.

See the Wikipedia entry http://en.wikipedia.org/wiki/Retronym for more examples.

Often confused with BackroNym and AproNym.