barium
Concise Oxford English Dictionary © 2008 Oxford University Press:
barium /ˈbɛːrɪəm/
▶noun the chemical element of atomic number 56, a soft white reactive metal of the alkaline earth group. (Symbol: Ba)
■ Medicine a mixture of barium sulphate and water, opaque to X-rays, which is swallowed to permit radiological examination of the stomach or intestines.
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