[tho.rax] n, pl tho.rax.es or tho.ra.ces [ME, fr. L thorac-, thorax breastplate, thorax, fr. Gk thorak-, thorax] (15c) 1: the part of the mammalian body between the neck and the abdomen; also: its cavity in which the heart and lungs lie
2: the middle of the three chief divisions of the body of an insect; also: the corresponding part of a crustacean or an arachnid