Definition of: ischium

(is′kē·əm) noun plural ·chi·a (-kē·ə)
1. Anat. The posterior part of the pelvic arch; in man, the part of the hip bone on which the body rests when sitting.
2. Zool. The third joint of any limb or lateral appendage in crustaceans.
3. Entomol. A side of the thorax in insects. Also is·chi·on (is′kē·ən). [<L <Gk. ischion hip, hip joint <ischys strong]
—is·chi·at·ic (is′kē·at′ik) or ·ad·ic (-ad′ik), is′chi·ac (-ak) or is′ki·al (-əl) adjective