internal has 6 distinct synonyms spread across 4 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 external.
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.
happening or arising or located within some limits or especially surface
“internal organs”
occurring within an institution or community
“intragroup squabbling within the corporation”
Synonyms, antonyms and the broader and narrower relations for internal come from Princeton University’s WordNet. Full sources and licences.