Which term is derived from a root meaning 'sac' in a medical context?

The term derived from a root meaning 'sac' in a medical context is indeed the one that relates to bursae, which are small, fluid-filled sacs that act as cushions between bones and tendons or muscles around the joints. The root "burs/o" is used in medical terminology to refer to these structures, often seen in conditions related to joint inflammation such as bursitis.

The other roots provided relate to different anatomical structures or concepts. The root "calc/o" pertains to calcium or calcification, "bronch/o" refers to the bronchi or air passages in the lungs, and "brachi/o" pertains to the arm. Therefore, "burs/o" is the only option that directly links to the meaning of 'sac,' making it the correct choice for this question.