Cattywhompus
From the archaic Cattus-Whompus (Greek in nature) for the cowherd who was wedded to the daughter of the cousin of the son of Aries (the parents of whom were Catius and Whompius).  Hence, the term was created to describe any of the Grecian cowherds who were descended from the original Catius.
This original definition gradually evolved into our more modern definition: the brand of any number of nonexistent products one may search to find in a place of trade.
You: Excuse me sir, do you have the latest Cattywhompus bag?
Clerk: Let me check our inventory.
You: Oh, I have most eagerly awaited the newest addition to the Cattywhompus line of products.