Calculus

Calculus is the hard substance that plaque forms on your teeth if it’s not removed – otherwise known as “tartar.” It can also refer to a hard mass of some kind, often one in the kidney or the bladder.

The name comes from the Latin word for “pebble,” which is why it’s also used to refer to the branch of mathematics, as stones were once used as a rudimentary calculation tool.

Why I Looked It Up

In a NY Times Connections puzzle, the clues were:

• Calculus
• Cavity
• Plaque
• Tartar

The category was titled “Concerns for a Dentist.”

I had never heard of the word being used in a medical context before. Also note that “Tartar” is also there, which is redundant.