Definitions:
a broad piece of metal or another suitable material, held by straps or a handle attached on one side, used as a protection against blows or missiles.

a person or thing providing protection

a large rigid area of the earth's crust, typically of precambrian rock, which has been unaffected by later orogenic episodes, e.g. the canadian shield.

protect from a danger, risk, or unpleasant experience

remain apart from others for a period of time in order to avoid catching an infectious disease to which one may be particularly vulnerable