Final answer:
The main part or foundation of a medical term is the word root.
Step-by-step explanation:
The main part or foundation of a medical term is the word root. An anatomical term is made up of roots, prefixes, and suffixes. The root of a term often refers to an organ, tissue, or condition, while the prefix or suffix describes the root. For example, in the medical term 'hypertension,' the root word 'tension' refers to pressure, and the prefix 'hyper-' means 'high' or 'over,' so 'hypertension' means abnormally high blood pressure.