cortex

noun

cor·​tex ˈkȯr-ˌteks 

plural cortices ˈkȯr-tə-ˌsēz  also cortexes

1

a(1)

: the outer or superficial part of an organ or bodily structure (such as the kidney, adrenal gland, or cerebellum or a bone)

especially : cerebral cortex

(2)

: the proteinaceous usually pigmented layer of a hair below the cuticle

b

: the outer part of some organisms (such as paramecia)

2

: a plant bark or rind (such as cinchona) used medicinally

3

a

: the typically parenchymatous layer of tissue external to the vascular tissue and internal to the corky or epidermal tissues of a green plant

broadly : all tissues external to the xylem

b

: an outer or investing layer of various algae, lichens, or fungi

Examples of cortex in a Sentence

Recent Examples on the Web

The researchers used a special kind of PET scan to detect changes in acetylcholine levels in the anterior cingulate cortex, a brain region that's important for making decisions and detecting errors. —Jon Hamilton, NPR, 22 Oct. 2025

Minutes later, the cortex, which is involved in more conscious, high-order thinking, follows suit. —Yasemin Saplakoglu, Quanta Magazine, 17 Oct. 2025

In the older examples of NOVA1, the metal disrupted neurons in the cortex and thalamus—two brain regions largely responsible for speech and language development. —Andrew Paul, Popular Science, 15 Oct. 2025

The study found that, on average, the men had a 56% loss of a specific type of neuron in the frontal cortex, the region most affected by CTE. —The New York Times News Service Syndicate, San Diego Union-Tribune, 14 Oct. 2025

Word History

Etymology

Latin cortic-, cortex bark — more at cuirass

First Known Use

circa 1676, in the meaning defined at sense 1a(1)

Phrases Containing cortex

• cerebral cortex
• piriform cortex
• prefrontal cortex
• pyriform cortex
• visual cortex

Rhymes for cortex

• vortex
• neocortex

Kids Definition

cortex

noun

cor·​tex ˈkȯr-ˌteks 

plural cortices ˈkȯrt-ə-ˌsēz  or cortexes

1

: an outer or surrounding layer of an organ or body part

the cortex of the kidney

especially : the outer layer of gray matter of the cerebrum

2

: the layer of tissue outside the xylem and phloem and inside the corky or epidermal tissues of a vascular plant

also : all tissues external to the xylem

Medical Definition

cortex

noun

cor·​tex ˈkȯr-ˌteks 

plural cortices ˈkȯrt-ə-ˌsēz  also cortexes

1

a

: the outer or superficial part of an organ or body structure (as the kidney, adrenal gland, or a hair)

especially : cerebral cortex

b

: the outer part of some organisms (as paramecia)

2

a

: a plant bark or rind (as cinchona) used medicinally

b

: the peel of any of several fruits

—used especially in the writing of medical prescriptions