single has 10 distinct synonyms spread across 6 of its 10 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 2 recorded opposites are double, multiple.
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 usually only one row or whorl of petals
“single chrysanthemums resemble daisies and may have more than one row of petals”
existing alone or consisting of one entity or part or aspect or individual
“upon the hill stood a single tower”
a base hit on which the batter stops safely at first base
hit a single
“the batter singled to left field”
1 of the 10 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for single.
Synonyms, antonyms and the broader and narrower relations for single come from Princeton University’s WordNet. Full sources and licences.