“Poppycock” is nonsense, rubbish, empty prattle, or claptrap, and was, in the last century, often used as an exclamation of disagreement.
The word originated around 1852, in the US, probably introduced by Dutch immigrants from the Dutch word poppekak and soon morphed into “poppycock.”
An oft-repeated theory is that the word came from the Dutch word pappekak, meaning “soft excrement,” but the Oxford English Dictionary states there is no such word in the Dutch language. There is, however, the very similar word, poppekak, which was once used to mean “excessive religious zeal.” What a difference one vowel makes!
Well, yes, excessive religious zeal is pretty nonsensical, so I can accept a connection.
One source says that the literal meaning of the word poppekak is “as fine as powdered doll shit.” The first half of the word is the Dutch pop for a doll (which could be related to a term of endearment, “poppet”). The second half is essentially the same as the Old English “cack” for excrement.
But pop is Dutch and “cack” is English. I don’t see how they can be welded together to come up with the Dutch word poppekak. Still, this kind of speculation is what makes research on weird words so interesting.
There’s no link to the sense of “cock” meaning rubbish (as in phrases like “that’s a load of old cock”), but there’s no doubt that poppycock is something of little value.
Poppycock is a brand of candied popcorn, though after learning of the name’s probable origin, I don’t think I want to eat any of it.