The cranial index refers to the measurement of the width and length of the skull, which is an important aspect of anthropological and biological studies. It is often used to differentiate between different racial or ethnic groups. There are several synonyms for the cranial index, including cephalic index, skull index, and craniometry. These terms all relate to the measurement of the skull, but may have slightly different applications or focus areas. Other related terms are also used in this field, such as facial index, which refers to the measurement of the face. Overall, the study of cranial anatomy and its measurement techniques remains a key area of research in anthropological and biological sciences.