Retronym
Etymology
Coined by Frank Mankiewicz and popularized by the columnist William Safire in the early 1980s: retro- "backward" (Latin) plus -onym "name" (Greek "onoma"). The word itself performs its meaning — a name for names created in hindsight.
noun · /RET-roh-nim/
A new name coined for an old thing to distinguish it from a newer version.
What it names
The linguistic fossil record of progress — every "acoustic guitar," "snail mail," or "landline" marks the moment a newcomer forced the original to be renamed.
Example
Nobody said "analog clock" until digital ones arrived and made the retronym necessary.
Related idea
A neologism is simply any newly minted word; a retronym is the narrower case of renaming something that already had a perfectly good name until technology moved on.
See also