inside has 10 distinct synonyms spread across 7 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 one recorded opposite is outside.
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.
relating to or being on the side closer to the center or within a defined space
“he reached into his inside jacket pocket”
2 of the 10 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 inside.
Synonyms, antonyms and the broader and narrower relations for inside come from Princeton University’s WordNet. Full sources and licences.