Why are nonsweet wines called "dry"?

What are Dry Wines?

Dry wines, also sometimes called "Table Wines", are wines which do not have an appreciable amount of residual sugar present in the finished, bottled wine. Because they do not have much or any sugar in the wine, they are not sweet. In other words, "dry", when referring to wine, basically means the opposite of "sweet".

One important note: This terminology is sometimes confusing to beginners for a very good reason. Many full-bodied red wines are high in tannins, naturally occurring compounds in grapes which contribute to the structure and texture of the wine. Tannins are generally described as having a drying, almost gritty or sandy texture in the mouth. People who are new to wine often describe these wines as very dry because the coarse tannins feel dry and astringent in their mouth. While this is a perfectly acceptable way to describe the sensation of tasting these wines, it can get confusing. In fact, even some sweet red wines like Port can have tannins, despite the sweetness of the wine. So it is best to describe these wines as tannic or to have drying tannins, not as a dry wine necessarily.

http://www.wine-tastings-guide.com/dry-wines.html

It is strange to call a liquid "dry", when by their very definitions liquids are wet. Why don't they call these wines either "sweet" or "non-sweet".

One theory is that sugar stimulates the saliva glands and leaves the mouth wet. Acids, on the other hand, have an astringent quality that leaves the mouth feeling dry. Winemakers, being very clever, know that consumers prefer not to call their wines "acidic" so they are labeled as "dry".

https://en.wikipedia.org/wiki/Sweetness_of_wine