introduction has 17 distinct synonyms spread across 4 of its 7 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.
the act of beginning something new
“they looked forward to the debut of their new product line”
formally making a person known to another or to the public
a basic or elementary instructional text
a new proposal
“they resisted the introduction of impractical alternatives”
the act of starting something for the first time; introducing something new
“she looked forward to her initiation as an adult”
Synonyms, antonyms and the broader and narrower relations for introduction come from Princeton University’s WordNet. Full sources and licences.