noun

• (uncountable) The state of being contained.
• (uncountable, countable) The state of containing.
• (obsolete, uncountable, countable) Something contained.
• (uncountable, countable) A policy of checking the expansion of a hostile foreign power by creating alliances with other states; especially the foreign policy strategy of the United States in the early years of the Cold War.
• (countable) A physical system designed to prevent the accidental release of radioactive or other dangerous materials from a nuclear reactor or industrial plant.
• (countable, mathematics) An inclusion.