A small otherworldly creature that fits in the palm of your hand. The humans of this world hunt grumbs in the spring (prime Grumb season) but only the bravest of adventures venture into the retarded forest (home to all horrific otherworldly beings)
"No son of mine shall venture into the retarded forest"
"If you want safe passage through the retarded forest you must pay me 3 Grumbs"
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).