Most words develop abstract meanings from concrete ones, but garb is different: it developed the other way around.
Garb initially meant “stylish in looks or bearing” in English, a synonym of elegance or grace. It came from the Italian word garbo, meaning “grace, charm, good manners,” but it also had a more concrete use, meaning “form” or “contour of a ship’s hull.” This last meaning may have developed from a dialectal word for “model of a ship’s hull” that ultimately traces back to the Arabic word qālib meaning “mold” or “shoemaker’s last.”
Early English dictionaries included entries for garbo as a borrowing spelled as it would be in Italian:
GARBO, grace, handsomnes, finenes, neatenes: also a garbe, a propernes, a comeliness
— John Florio, A Worlde of Wordes, 1598
Several decades later, the spelling had shifted to garbe:
Garbe, a sheaf of corn, from the french word gerbe, a bundle; also handsomness, graceful carriage, from the italian word garbo
— Edward Phillips, The new world of English words, or, A general dictionary containing the interpretations of such hard words as are derived from other languages, 1658
These early dictionaries missed an important usage of garb, however. Sometimes it simply meant “style” or “fashion” or “prevailing mode,” and Shakespeare used it that way, when Hamlet welcomes the troupe of players:
Gentlemen, you are welcome to Elsinore. Your hands, come then. Th' appurtenance of welcome is fashion and ceremony. Let me comply with you in this garb—lest my extent to the players, which, I tell you, must show fairly outwards, should more appear like entertainment than yours.
Shakespeare also used garb when referring to a person’s accent, in Henry V:
You thought, because he could not speak English in the native garb, he could not therefore handle an English cudgel: you find it otherwise; and henceforth let a Welsh correction teach you a good English condition.
Garb then made the leap to the concrete, referring to “style or manner of dress.” It wasn’t until the latter part of the 1600s that garb meaning “clothing” became common.
Today, garb connotes specificity. One rarely says “I always admired her garb,” or “The children wore their best garb to the party”; garb is nearly always modified to make it refer to a very particular type of clothing:
the traditional garb of the herdsmen out on the steppes
additional leg garb included over-the-knee boots, stretch tights with shoes attached and snug pants