noun. A condition of the head that is highly correlated with being dumb as a box of rocks.
Real citation: “I also think Wooing is related to the crowd behavior I used to see when I was a music critic. By that I mean rampant dunderheaditude, usually (but not always) caused by the ingestion of large quantities of grain-based beverages.”
(Mike Redmond, June 14, 2007, The Southside Times, http://s41171.gridserver.com/?p=172#more-172)
Made-up citation: “I have had it! You think my dunderheaditude is because I’m a guy. Well, maybe it’s just part of who I am, along with my reverse moral fiber.”