Poppycockish is a word primarily used to describe something as foolish, nonsensical, or ridiculous. There are a number of synonyms that might be used in place of poppycockish such as absurd, nonsensical, or preposterous. Other potential options could include fantastical, far-fetched, or implausible. Alternatively, one might describe something as ludicrous, asinine, or even just plain silly. If one is looking to add a bit of specificity to their description, they might also use words like ungrounded, illogical, or irrational. Ultimately, when looking for a synonym for poppycockish, it's all about finding the exact right word to capture just how ridiculous something truly is.