Definition of thorax
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
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Time Traveler for thorax
The first known use of thorax was in the 15th century
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