WordNet records no synonym and no antonym for containment. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a policy of creating strategic alliances in order to check the expansion of a hostile power or ideology or to force it to negotiate peacefully
“containment of communist expansion was a central principle of United States' foreign policy from 1947 to the 1975”
(physics) a system designed to prevent the accidental release of radioactive material from a reactor
the act of containing; keeping something from spreading
“the containment of the AIDS epidemic”
Synonyms, antonyms and the broader and narrower relations for containment come from Princeton University’s WordNet. Full sources and licences.