thorax

noun

tho·​rax ˈthȯr-ˌaks 

plural thoraxes or thoraces ˈthȯr-ə-ˌsēz 

1

: the part of the vertebrate body between the neck and the abdomen

If you count the vertebrae in the necks and thoraxes of mice and chickens, you will find that a mouse has seven neck and 13 thoracic vertebrae, a chicken 14 and seven, respectively.

—Matt Ridley

also : thoracic cavity

The thorax is evaluated for fluid at the flanks and for pneumothorax anteriorly.

—Christoper L. Moore

2

: the middle of the three chief divisions of the body of an insect

Of nearly a million described species of insects, none has a biramous appendage, and nearly all have exactly three pairs of limbs on the thorax.

—Stephen Jay Gould

This haunting pitch issues from drum tissue stretched over the thorax of the male annual cicada …

—Ted Williams

also : the corresponding part of a crustacean or an arachnid

The brown recluse spider … is brown and has fuzzy body hair and a dark violin- or pear-shaped band on the dorsum of its thorax.

—Peter F. Weller

Examples of thorax in a Sentence

Recent Examples on the Web

At around 3 to 4 millimeters, the adults have a tan thorax, and the abdomen is split with black on top and gray on the underside. —Bestreviews, Mercury News, 18 Apr. 2025

Carpenters have yellow fuzz on their thorax, but their abdomens are shiny, black, and hairless. —Katie Akin, Southern Living, 26 Apr. 2025

The text stops mid-sentence in case 48 at the arms and upper thorax. —Emilie Le Beau Lucchesi, Discover Magazine, 4 Feb. 2025

Strut that runway with your arms and legs poking out of your thorax and looking sooo long! —Julie Sharbutt, The New Yorker, 16 Jan. 2025

Word History

Etymology

Middle English, from Latin thorac-, thorax breastplate, thorax, from Greek thōrak-, thōrax

First Known Use

15th century, in the meaning defined at sense 1

Rhymes for thorax

• prothorax

Kids Definition

thorax

noun

tho·​rax ˈthō(ə)r-ˌaks 

ˈthȯ(ə)r-

plural thoraxes or thoraces ˈthōr-ə-ˌsēz 

ˈthȯr-

1

: the part of the body of a mammal between the neck and the abdomen

also : its cavity in which the heart and lungs lie

2

: the middle of the three main divisions of the body of an insect

Medical Definition

thorax

noun

tho·​rax ˈthō(ə)r-ˌaks, ˈthȯ(ə)r- 

plural thoraxes or thoraces ˈthōr-ə-ˌsēz, ˈthȯr- 

1

a

: the part of the body in vertebrates that is situated between the neck and the abdomen and supported by the ribs, costal cartilages, and sternum

b

: thoracic cavity

2

: the middle of the three chief divisions of the body of an insect

also : the corresponding part of a crustacean or an arachnid