Final answer:
The correct word to complete the medical term 'anter/o/______/ior' is 'posterior', making the term 'anteroposterior' which refers to something related to both the front and the back of the body.
Step-by-step explanation:
The word part that completes the medical term meaning pertaining to the front and to the back, anter/o/posterior/ior, is posterior. Therefore, the complete term 'anteroposterior' refers to something that is related to both the front and the back of the body. For instance, the term can be used to describe an X-ray that captures images from both the front and the back.
In anatomical terminology, 'anterior' or 'ventral' refers to the front or direction toward the front of the body, while 'posterior' or 'dorsal' refers to the back or direction toward the back of the body. Other related terms include 'superior' or 'cranial' for a position above or higher than another part of the body, 'inferior' or 'caudal' for a position below or lower, 'lateral' for the side or direction toward the side, and 'medial' for the middle or direction toward the middle of the body.