means An abnormal enlargement of part of the body, usually from a buildup of fluid as tissue reacts to injury, infection, or irritation.

from From the Old English verb 'swellan,' meaning to grow larger or rise up — the same root behind 'swell' for ocean waves and for that puffed-up sense of pride. It belongs to a wider Germanic family (compare Old Norse 'svella' and German 'schwellen'), all circling the idea of something bulging or rising beyond its usual size. The body's version simply borrows the imagery of a tide coming in.