means Relating to the thorax — the chest, the part of the body between the neck and the abdomen that houses the heart and lungs.

from From Greek 'thorax,' which originally meant a breastplate — the piece of armor that shielded a warrior's chest. The same word came to name the body part the armor protected, and Latin borrowed it as 'thorax' before it filtered into medical English. So the word still carries its old battlefield logic: the chest as the body's own breastplate, guarding the vital machinery within.