WordNet records no synonym and no antonym for sacrament. It is the only member of its synset, 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 formal religious ceremony conferring a specific grace on those who receive it; the two Protestant ceremonies are baptism and the Lord's Supper; in the Roman Catholic Church and the Eastern Orthodox Church there are seven traditional rites accepted as instituted by Jesus: baptism and confirmation and Holy Eucharist and penance and holy orders and matrimony and extreme unction
Synonyms, antonyms and the broader and narrower relations for sacrament come from Princeton University’s WordNet. Full sources and licences.