These warm garments were originally heavy blankets used by horse trainers to induce sweating, hence the name. But people didn't wear them at first - racehorses did!
First recorded in 1828, sweaters were fashioned to fit around a horse's body and were part of a routine workout on the track. Thirty years later, the sweat-producing flannel underclothing athletes wore to lose weight was also called a "sweater."
By the 20th century, the sweater had become fashionable. First, it was a woolen vest or jersey used in rowing, and then a woolen outer garment worn by anyone looking for comfort and warmth. Today, you see it on the fast track or the slow track.
"Slipshod," an expression for sloppy or careless, has nothing to do with horses. But it has a lot to do with house slippers.
Fifteenth-century slip-shoes, as they were called, were among the earliest in use, and they were designed for indoors. Made of a thin felt, slip-shoes had no heels or fasteners; they were easy to slip on or off and they didn't damage floors.
But some people walked outdoors in them, and by 1580, any person wearing a loose slipper in public places was considered shameless and careless in his or her appearance, or "slip-shod" (literally meaning "clad with slippers").
The phrase, "to be gussied up," or dressed in one's finest clothes, derives from the triangular pieces of fabric called "gussets" placed in garments to give them strength and a better fit.
It was the knights of the Middles Ages who started the tradition by inserting the soft pads between two pieces of mail armor so they could have more comfort when moving about.
In time, gussets (meaning husks or shells) were used as inserts in suits and gowns, usually on the shoulders. Today, someone with gussets may have such improvements in their comfort and look that they're considered "all gussied up."
SOURCES: 'A Browser's Dictionary,' by John Ciardi; 'Why You Say It,' by Webb Garrison; The Oxford English Dictionary; 'Dictionary of Word Origins,' by Joseph Shipley; 'The Encyclopedia of Word and Phrase Origins,' by Robert Hendrickson; 'Morris Dictionary of Word and Phrase Origins,' by W. and M. Morris; 'The Barnhart Dictionary of Etymology,' by Robert K. Barnhart; 'The Story Behind The Words,' by Morton Freeman; 'Horsefeathers,' by Charles E. Funk.