The word itself is of French derivation and originally meant "linen goods". The actual word can be traced back in history as coming from "linum", the word used for flax.
Now "linen goods" does not bring to mind any images of the scantily clad women we see today so it seems as if it went through some kind of transition. In 18th and 19th century England, it was considered improper for a woman to openly refer to her underwear in normal conversation and polite euphemisms were used instead.
The French of the time simply referred to "women's underwear" with the French word lingerie as a substitute for that which you did not openly discuss. Lingerie of the time had the sole purpose of absorbing sweat and other body fluids in an attempt to preserve the much more expensive outer wear. The clothes of the day were not mass produced in China; they were mostly handmade to order by a family member or a professional seamstress etc. The point being, outer wear was considered expensive, hard to come by, and therefore had to be looked after and kept clean. Underwear was therefore made of cheap linen which could be washed often and replaced much more easily and affordably.
So how did the French word lingerie find its way into the English language? Corsets were already in use by Victorian women during this time but they used the word 'corset' as is. The corset is therefore not responsible for popularizing the word lingerie. It comes from another French invention called the brassiere which became known to the English and Americans during the roaring twenties, spurred on by early Hollywood films which threw a spot light on beautiful women with desirable bodies in sexy dresses. Soon everybody was talking about the gorgeous movie stars and women wanted to shape their bodies and style their hair to resemble the screen icons of the day. The brassiere became the hot item and the French became seen as the "knowledgeable source" of desirable women's underwear.
The brassiere was originally designed only to support the breasts but its versatility was quickly recognized and over a relatively short time its use branched out to cover the many needs of the day. The question for women was; what did you want to do with your breasts? Just provide support, support and lift etc. The versatile brassiere could be designed to fit any need. Styles changed from flat to pointy to naturally rounded. Men took notice. Women noticed that men were interested which just fueled the fire.
Stockings, suspenders and brassiere became collectively referred to using the French word "lingerie" because it sounded more exotic and mysterious than any wording the English speaking marketing people could come up with. Thus the word lingerie became popular and ingrained as the term used to describe "special women underwear" as being something different to functional women underwear.
Shaping peoples' bodies to emphasize certain features is hardly a new idea. Paintings from Crete (ancient Greece) depict Minoan women wearing a type of corset to slim the waist and push out the breasts to make a feature of them.
This is typical of the changing and different viewpoints among various cultures and times. Most of today's men would love to bring back the Minoan dress code for women. Their culture did also have its advantages. Women were treated as equals and garnered as much respect from men as they did admiration.