double has 26 distinct synonyms spread across 13 of its 21 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. Its one recorded opposite is single.
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.
used of flowers having more than the usual number of petals in crowded or overlapping arrangements
“double chrysanthemums have many rows of petals and are usually spherical or hemispherical”
used of homologous chromosomes associated in pairs in synapsis
bend over or curl up, usually with laughter or pain
“He doubled and vomited violently”
do double duty; serve two purposes or have two functions
“She doubles as his wife and secretary”
bridge: make a demand for (a card or suit)
make or do or perform again
“He could never replicate his brilliant performance of the magic trick”
a base hit on which the batter stops safely at second base
“he hit a double to deep centerfield”
a stand-in for movie stars to perform dangerous stunts
“his first job in Hollywood was as a double for Clark Gable”
someone who closely resembles a famous person (especially an actor)
“he could be Gingrich's double”
a quantity that is twice as great as another
“36 is the double of 18”
3 of the 21 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for double.
Synonyms, antonyms and the broader and narrower relations for double come from Princeton University’s WordNet. Full sources and licences.