Linguistics question: what's the process by which new terms replace perfectly serviceable old terms?

[KneadToKnow]

I’m utterly puzzled by how the term “underwater” seems to have recently replaced the perfectly serviceable term “upside down” to describe situations such as those where a mortgagee owes more to the lender than the mortgaged property is worth.

Every time I hear it, I think, “There was already a term for that, moron.” But I’m not here to discuss that, specifically.

I’m sure this happens from time to time, and I’m wondering if there’s a term for this process.

[Indistinguishable]

What’s so moronic about it? Are you unhappy that there are synonyms?

[nudgenudge]

The question calls to mind the excellent book The Unfolding of Language (often recommended by other posters on this board, I see). It describes various creative and destructive impulses which force all languages to be in a state of constant, gradual change.

A change such as “underwater” becoming preferred to “upside down” is just a minor example. New forms start out as arresting metaphors, but the power of the metaphors gets eroded with use, to the point that they become just stock phrases (and sometimes, they just become ordinary words whose original meaning is obscure to all but linguistic archaeologists). And then some bright spark comes up with a novel metaphor which takes people’s fancy.

There’s a brilliant passage in the aforemetioned book in which the author presents a raher dry and tedious news report and then points out that the everyday language used in the report is in fact full of imagery and metaphor, but we don’t notice it because the original metaphorical meaning has become “fossilized”.

[Strainger]

Huh. I thought “underwater” meant owing more than it’s worth, whereas “upside-down” meant that the current value is less than what you bought it at. But I could be wrong.

[brianmelendez]

One example of the phenomenon that the OP is asking about is a retronym:

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.

“Some Retronyms in English,” ceafinney: retronyms; quoting American Heritage Dictionary.

A term coined as a modification of a referent originally used alone, to distinguish it from a later contrastive development.

World Wide Words, http://www.quinion.com/words/weirdwords/ww-ret1.htm.

a new word or phrase coined for an old object or concept whose original name became used for something else.

Wikipedia, Retronym - Wikipedia.

Newly created contrast sets because of inventions
|||||, call it X
invent variant /////, call it AX
need word as hypernym, use X
then give new name to original X: BX

"Lecture Notes: Linguistics 181,” http://www.icsi.berkeley.edu/~fillmore/ling181/notes.0506.html.

The original word becomes the hypernym, and the original concept becomes a protonym. Some examples of retronyms:

What was once called simply / is now called / because now it needs distinguishing from:

airplane / propeller airplane / jet airplane
baseball / day baseball / night baseball
business / brick-and-mortar business / online business, e-business
clock / analog clock / digital clock
coffee / regular coffee, caffeinated coffee / decaffeinated coffee
Coke / classic Coke, real Coke / new Coke
Great War, World War / World War I / World War II
guitar / acoustic guitar / electric guitar
mail / snail mail, postal mail, paper mail / electronic mail
movie / silent movie / talking movie
reality / meatspace / cyberspace
search / eyeball search, visual search / computer search, electronic search, online search
skiing / snow skiing, downhill skiing / water skiing
telephone / corded telephone / cordless phone, wireless phone

For a good discussion of retronyms (and the word’s etymology), see http://www.quinion.com/words/weirdwords/ww-ret1.htm; see also Retronym - Wikipedia. For a list of retronyms, see ceafinney: retronyms; see also Retronym - Wikipedia.