Noun
(medicine) A preparation of barium sulfate (a radioopaque compound) which the patient ingests for the purpose of producing clear radiographs of the esophagus, stomach, and duodenum.
(medicine) A diagnostic procedure based on observing the barium meal's progress in the digestive tract.
(espionage) The deliberate release of traceable information to a suspect to see whether they leak it.
Source: en.wiktionary.org