Immune system
Etymology
From Latin "immunis" (exempt), built from "in-" (not) and "munus" (duty, service, tax). In Rome it meant being excused from public obligations; the medical sense borrows that image of exemption — a body "exempt" from a disease it has learned to resist.
noun phrase · /ih-MYOON SIS-tuhm/
The body’s network of cells and organs that detects and destroys invaders and abnormal cells.
What it names
A handle for the whole distributed defense force — not one organ but a coordinated system spread through the body.
Example
A good night’s sleep does more for your immune system than most supplements.
Related idea
Immunity is the state of being protected; the immune system is the machinery that produces and maintains that state. It splits into innate immunity — fast, general defenses you’re born with — and adaptive immunity, the slower, learned response that remembers specific invaders.