similar has 6 distinct synonyms spread across 3 of its 5 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 dissimilar.
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.
marked by correspondence or resemblance
“similar food at similar prices”
resembling or similar; having the same or some of the same characteristics; often used in combination
“suits of like design”
capable of replacing or changing places with something else; permitting mutual substitution without loss of function or suitability
“interchangeable electric outlets”
1 of the 5 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 similar.
Synonyms, antonyms and the broader and narrower relations for similar come from Princeton University’s WordNet. Full sources and licences.