Final answer:
The word built from the prefix 'thym/o' that means a tumor of the thymus gland is 'thymoma'. This gland is important for immune system function and is the site where T cells mature.
Step-by-step explanation:
To build a word using the prefix thym/o that means tumor of the thymus gland, we use the term thymoma. The thymus gland is an organ involved in the development of T-cells and is vital for the adaptive immune system. A thymoma is typically a benign tumor but can sometimes behave malignantly.
The thymus gland is located in the chest, behind the breastbone, and in front of the heart. The word 'thymoma' is composed of the root 'thym/o,' meaning thymus, followed by the suffix '-oma,' which denotes a tumor or neoplasm. Therefore, thymoma directly translates to a tumor involving the thymus gland.