A useful picture here comes straight from the word's history: a breastplate, the piece of armour a soldier straps over the middle of his body. Whatever that plate covers is what this word names — not the head, not the belly, the section in between, together with the room behind it. In a person that room holds the heart and the lungs. On an insect the same middle section is where all six legs and the wings are fixed. Same place on the body, two very different creatures.
Latin thorax, from Ancient Greek θώραξ, a breastplate or cuirass — the armour worn over exactly this part of the body.
拉丁文 thorax，再往前是古希臘文 θώραξ，原意是「胸甲」。護具蓋住的就是身體的這一段，所以這個字後來直接拿來指那個部位。
Wiktionary entry for thorax, etymology_text: 'From Latin thorax, from Ancient Greek θώραξ (thṓrax, "a breastplate, cuirass, corslet").' (kaikki:3f6f69a190036ae4:873214577)
One branch
身體中間那一段
兩個意思其實是同一個定義用在不同生物上：頭以下、腹以上的那一段。差別只在裡面裝什麼、外面接什麼。
noun · C1
The part of the body between the neck and the stomach area, and the space inside it that holds the heart and the lungs. This is the medical word; in everyday talk people say 'chest'.
胸腔