(n.) nonsense, gibberish
Something smells a bit iffy about poppycock. People have been using it to mean “nonsense” or “useless blather” since the early 1800s, when it first began to appear in the colloquial English of the northeast United States. But how did it get there in the first place?
According to several online sources—including the Merriam-Webster Dictionary—poppycock is a corruption of the Dutch word pappekak, a compound of pap, meaning “soft, chewed up food”, and kak, meaning, well, “cack”. Put together, pappekak, as the Oxford English Dictionary so eloquently explains, means something along the lines of “excrement as soft as porridge”. And on that basis it’s easy to see how the word came to describe something of little value.
But as the OED also points out, “no such word appears to be attested in Dutch”. That is to say, pappekak is a linguistic conjecture, a word only presumed to exist by keen etymologists clutching for possible origins of poppycock. So if porridgey poop isn’t quite right (which it isn’t in more ways than one, certainly), then what is?
Bizarrely, a more plausible explanation is that poppycock comes from from the Dutch poppekak, meaning “doll excrement”. As odd as that might sound, poppekak is actually a genuine Dutch word attested in an old idiomatic phrase—zo fijn als gemalen poppekak, or “as fine as powdered doll’s excrement”—once used to describe someone showing what the OED calls “excessive religious zeal.”
So we can only presume that Dutch immigrants arriving in America in the early 1800s brought this peculiar expression with them. There, poppekak eventually morphed into poppycock and, perhaps through association with the pulpit-thumping preachers of the time, ultimately came to mean “empty prattle”, “claptrap”, and “nonsense”.