We have beachwear and townwear in English, which connect apparel and place (and perhaps appropriateness). There’s sportswear and skiwear and swimwear, which are connected with activities. There’s even outerwear and, of course, underwear, terms that describe the garments rather than their function. English also furnishes supremely practical terms like footwear and headwear, which identify the body parts covered by the named apparel.
Of all of these, perhaps only one has been used with reference to two very different etymological rationales: loungewear, which today means “informal clothing usually designed to be worn at home,” initially meant something else entirely.
In the late 1800s, clothes appropriate for wearing in a lounge would seem strikingly formal for us today. Back then, lounges were either synonymous with parlors or hotel lobbies, but in each case, these were spaces where more formal attire was expected.
The clothing worn in such spaces would be technically informal—but this was a time when “formal” specifically meant white tie and tails for gentlemen. This is why the term lounge suit is still used in British English to refer to what most of us would call a business suit today. In fact definition 1c of lounge in the Oxford English Dictionary is:
Elliptical for lounge-coat, -jacket, -suit
It’s clear that the lounge in lounge suit in this instance comes from the noun lounge, not from the verb meaning “to act or move idly or lazily,” a synonym of loaf. In fact, we can see that lounge wear was also used in this way, referring to relatively dressy clothes:
The members of each squadron are being measured for the jackets in their own localities by a visiting tailor from Aldershot. The coat is to be of easy fit, adaptable to lounge wear, and will be very acceptable to the force.
—Berrow’s Worcester Journal (Worcester, Eng.), 2 May 1896
Those who still prefer (as I do myself) a perfectly plain, self-colored cravat for lounge wear have been appeased by some new brown crapes, which are even more beautiful in one than the foulards….
—The Washington Post, 3 Oct. 1904
For business and lounge wear the only overcoat indorsed by good form this seasons is the plain long “Chesterfield.”
—Alfred Stephen Bryan, Detroit Free Press, 15 Oct. 1905
This original use of loungewear seems to have been missed by dictionaries; it’s found in neither the OED nor the massive and encyclopedic Webster’s Second edition of 1934. The loungewear we know today, of course, often pajamas or sweats, clearly derives not from the noun lounge but from its cousin, the verb.