The Collaborative International Dictionary
Prosoma
Prosoma \Pro*so"ma\, n.; pl. Prosomata. [NL., fr. Gr. ? before + ?, ?, body.] (Zo["o]l.) The anterior of the body of an animal, as of a cephalopod; the thorax of an arthropod.
Wiktionary
prosoma
n. (context zoology English) The front segment of a body which is divided into two or more segments, especially the cephalothorax of an arachnid.