sulcus

This term is primarily used in medical and biological contexts to describe a physical indentation or valley. In neurology, it specifically refers to the folds of the cerebral cortex, where it pairs with the gyrus (the ridge) to increase the surface area of the brain. It carries a clinical, precise connotation and is rarely used outside of anatomical descriptions.

Because it is derived from Latin, the word follows a specific irregular pluralization pattern. Instead of adding a standard English s, the ending changes to i to form the plural sulci, a common trait among Latin-based anatomical terms.