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

To keep the ants from wandering (or simply falling) off the treadmill, the scientists glued the thorax to a small pin. —Seriously Science, Discover Magazine, 22 Feb. 2017

Typically, the head, thorax and legs are dark brown and the abdomen is brownish black. —Natalie Neysa Alund, USA TODAY, 14 June 2023

An x-ray reveals a complete surprise to the attending physician, an anomaly wildly beyond the expectations of the typical anatomical variant: dozens of balls in the thorax. —Rebecca Kreston, Discover Magazine, 24 Mar. 2017

Dickman has found that lesser hairy-footed dunnarts (Sminthopsis youngsoni) and Wongai ningaui (Ningaui ridei)—small mouselike marsupials in Australian deserts—preferentially eat the abdomens and thoraxes of their insect, spider and centipede prey. —Stephanie Pappas, Scientific American, 11 Apr. 2023

Another intern taught her how to spread the jam evenly, monitor the drying process, then use tweezers to assemble the head, thorax, abdomen and wings. —Julia Moskin, New York Times, 9 Jan. 2023

By distorting the shape of the thorax, the orientation of the beating wings is changed. —Carl Engelking, Discover Magazine, 26 Mar. 2014

No dry-fly hatch in North America incites as much frenzy among trout flyfishermen as the emergence of Pteronarcys californicus —the giant stonefly (a.k.a. the salmonfly, a nickname that comes from the orange color on the thorax), in the Western trout rivers of the Rockies. —Keith McCafferty, Field & Stream, 16 June 2020

Bacteria and viruses settle into the crevices and cracks between thorax and head, and begin to multiply. —Rebecca Kreston, Discover Magazine, 9 May 2012

See More

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

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