confirmation has 4 distinct synonyms spread across 2 of its 5 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.
additional proof that something that was believed (some fact or hypothesis or theory) is correct
“fossils provided further confirmation of the evolutionary theory”
information that confirms or verifies
making something valid by formally ratifying or confirming it
“the ratification of the treaty”
a ceremony held in the synagogue (usually at Pentecost) to admit as adult members of the Jewish community young men and women who have successfully completed a course of study in Judaism
a sacrament admitting a baptized person to full participation in the church
Synonyms, antonyms and the broader and narrower relations for confirmation come from Princeton University’s WordNet. Full sources and licences.