IMMUNE SYSTEM -
Noun: A collection of cells and proteins that work to protect the body from potentially harmful, infectious micro-organisms (microscopic life-forms), such as bacteria, viruses, and fungi. The immune system also plays a role in the control of cancer and is responsible for the phenomena of allergy, hypersensitivity, and rejection problems after transplants.

The immune system has the skin as it's first line of defence but if micro-organisms penetrate it through cuts or the mucous membrane linings of the mouth, throat, eyes, intestines, etc. they soon encounter white blood cells called phagocytes (literally, "devouring cells"), which attempt to destroy them. They also encounter other types of white cells, called the Lymphocytes which are the most competent and versatile group of cells for getting rid of "unwanted guests".

Latin - in = not +

Latin - munis = obliging

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