The gem was cut into an exquisite eight-pointed shape.

eight-pointed 是由数词 eight（八）和名词 point（点、尖端）加上后缀 -ed 组成的复合形容词。point 在这里指"角"，-ed 表示"具有...特征的"，所以 eight-pointed 意思是"有八个角的"，即"八边形的"。