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First Known Use: 1665
 
Etymology
 
One day, the British scientist and “natural philosopher” Robert Hooke bent over a microscope that he’d constructed himself. He’d studied plenty of objects under the microscope before—the tip of a needle, a printed dot, snowflakes—but when he sketched and named this particular observation, he would take a word previously known for its religious connotations and bring it into the world of science.
 
Underneath the microscope was a piece of cork.
 
When magnified, Hooke saw that the cork had a series of shallow, walled boxes or “pores.” We now know that Hooke was seeing the xylem structure, or specialized tissue in vascular plants, of the dead cork. The story goes that the small boxes reminded the scientist of the rooms that monks stayed in, which were called cellula. Later, when Hooke wrote about and illustrated what he saw under the microscope in his 1665 book Micrographia: Or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon, he used the word cell to describe what he was seeing—the first known person to do so in this context. While cell theory as we know it today wouldn’t begin to develop for another century and a half, his book is the reason we use the word cell to describe the smallest functional unit capable of life.
 
Micrographia was a bestseller when it debuted, says Arlene Shaner, historical collections librarian at the New York Academy of Medicine. It was so popular that reprints were issued, as well as a second edition two years later. “People were astonished by this book,” she says. “People had not seen this. [Today,] we see everything magnified—the world that we can see into has been so expanded that we get very jaded on some level. And I think this book does a lot to reawaken that sense of wonder in the natural world.”