The word comes from British English and means: nonsense, rubbish, bosh, humbug, tommyrot, tripe, drivel, codswallop, poppycock, bollocks (another Britishism), bullshit, bunk, balderdash, horsefeathers, or any worthless stuff. It also means, of course, refuse given to hogs as food.
It originated around the mid-15th century, combining two words, hog and wash, and described ‘kitchen swill for pigs.’ By 1712, hogwash was also be used to describe cheap liquor; by 1773, it was applied to poorly written manuscripts. Today, almost anything that is badly done or ridiculous can be equated with this term for barnyard slop.
The synonyms for hogwash have interesting histories of their own. James McDonald, in Wordly Wise, (1984) writes that in the 19th century ”an inventor called Hiram Codd patented a new type of bottle with a glass marble in its neck. Mineral waters were sold in such bottles and, wallop being a slang term for fizzy ale, the contents became known as Codd’s Wallop.” In Norman W. Schur’s English English, the noun codswallop is defined as ‘hot air.’
The Oxford English Dictionary labels poppycock as US slang. Charles Farrar Browne, the humorist who went by the name of Artemus Ward, said in 1865: ”You won’t be able to find such another pack of poppycock gabblers as the present Congress of the United States,” a statement that no doubt has been expressed every year since then, and applied to every government in existence.
Horsefeathers came from the early building-trade, referring to the tapered boards laid to provide a flat surface for asphalt roof shingles, also called ”feathering strips.”
An Internet article on interesting phrases offered a different explanation. “Steamboats carried both people and animals. Since pigs smelled so bad they would be washed before being put on board. The mud and other filth that was washed off was considered useless “hogwash.” This explanation is itself hogwash, since the word came into use at least a couple of hundred years before steamboats. But I’ll give the writer points for imagination!