shortened has 6 distinct synonyms spread across 4 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.
shortened by or as if by means of parts that slide one within another or are crushed one into another
“a miracle that anyone survived in the telescoped cars”
Synonyms, antonyms and the broader and narrower relations for shortened come from Princeton University’s WordNet. Full sources and licences.