1865, American English, probably from Dutch dialect pappekak, from Middle Dutch pappe "soft food" (see pap) + kak "dung," from Latin cacare "to excrete" (from PIE root kakka- "to defecate").
Wow, poppycock literally means shit pabulum. I had no idea. Puts a new spin on https://www.google.com/search?q=poppycock&source=lnms&tbm=is....
But, that's a latin root, not greek.
Then again - it does suggest the same root: https://www.etymonline.com/word/*kakka-?ref=etymonline_cross...