from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A dullard; a blockhead.
from the GNU version of the Collaborative International Dictionary of English
- n. A dullard, or dull person; a blockhead; a numskull.
from The Century Dictionary and Cyclopedia
- n. A dull person; a blockhead.
thick + skull (Wiktionary)
That is a something that you should as you put it get through your thickskull.