Final answer:
The medical term for examining the stomach with an instrument is gastroscopy, which involves the use of an endoscope to view the stomach lining.
Step-by-step explanation:
The medical word that means the process of using an instrument to examine the stomach is gastroscopy. During a gastroscopy, a doctor inserts an endoscope, which is a flexible tube with a camera and light at the end, through the patient's mouth and down the throat into the stomach. The device allows the doctor to view the stomach lining and other parts of the upper gastrointestinal tract on a video screen. Procedures such as taking biopsies or removing polyps can also be performed during this examination.