festoon has 1 distinct synonym spread across 1 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.
a curtain of fabric draped and bound at intervals to form graceful curves
an embellishment consisting of a decorative representation of a string of flowers suspended between two points; used on pottery or in architectural work
flower chains suspended in curves between points as a decoration
Synonyms, antonyms and the broader and narrower relations for festoon come from Princeton University’s WordNet. Full sources and licences.
decorate with strings of flowers
“The public buildings were festooned for the holiday”