Q: Why is the word “dense” used to describe both an empty-headed person and a novel stuffed with too much information?
A: For hundreds of years, someone with a low gray-cell count has been described as “empty-headed” or “thickheaded.” And “dense” has been used for nearly as long to describe such a person or a novel overloaded with plots, characters, and description.
How can an empty head be described as “thick” or “dense”? Perhaps because knowledge can’t penetrate it.
When the adjective “dense” appeared in English in the late 16th century, it meant “having its constituent particles closely compacted together; thick, compact,” according to the Oxford English Dictionary.
The first OED citation is from a section on eye diseases in The Boock of Physicke, a 1599 translation of a medical work by the Dutch physician Oswald Gaebelkhover:
“When as the Cataracte is so dense and of such a crassitude [thickness] that heerwith they will not be soackede.”
In the 18th century, the adjective took on the figurative sense of being overwritten and unclear. The first Oxford citation is from a 1732 issue of Historia Litteraria, a monthly literary journal edited by the Scottish historian Archibald Bower:
“Sometimes the Author is not so properly concise, as dense, if I may use the Word. When the Subject is limpid of it self, he frequently inspissates [thickens] it, by throwing in a heap of Circumstances not Essential to it.”
In the early 19th century, the adjective came to mean stupid, as in this OED citation from an 1822 essay by Charles Lamb in the London Magazine: “I must needs conclude the present generation of play-goers more virtuous than myself, or more dense.”
The term “empty-headed,” which appeared in the early 17th century, describes someone “having or showing little intelligence; lacking sense; foolish, frivolous,” according to the dictionary.
The earliest Oxford citation is from The History of the World, a 1614 book by Sir Walter Raleigh: “Wise men depend vpon so many vnworthy and emptie-headed fooles.” (Raleigh wrote the history while he was in the Tower of London, awaiting execution.)
The term “thick-headed,” used figuratively to mean “dull of intellect; slow-witted, obtuse,” showed up in the early 19th century, according to the OED.
The dictionary’s earliest example is from The Good French Governess, an 1801 children’s novel by the Anglo-Irish writer Maria Edgeworth: “He was so ‘thick-headed at his book,’ that Mrs. Grace … affirmed, that he never would learn to read.”
English has many figurative adjectives and nouns for someone who’s not the sharpest knife in the drawer. Here are a few, with the earliest OED citations: “harebrained” (1548), “blockhead” (1589), “scatterbrained” (1804), “pea-brain” (1938), and “airhead” 1971.