confinement has 7 distinct synonyms spread across 2 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
concluding state of pregnancy; from the onset of contractions to the birth of a child
“she was in labor for six hours”
the act of restraining of a person's liberty by confining them
the state of being confined
“he was held in confinement”
the act of keeping something within specified bounds (by force if necessary)
“the restriction of the infection to a focal area”
Synonyms, antonyms and the broader and narrower relations for confinement come from Princeton University’s WordNet. Full sources and licences.