Definition of "dullard"

Oh! Richard of Bury, I sighed, for a sharp stone from your sling to pierce with indignant sarcasm the mental armour of these college dullards.

1880, William Blades, The Enemies of Books, page 41

Whereas some prodigies develop at an early age, Einstein did not exhibit any great genius as a young child. Some people thought he was a dullard.

1995, Temple Grandin, Thinking in Pictures: And Other Reports from My Life with Autism, Vintage Books, published 2006, page 211