section has 9 distinct synonyms spread across 8 of its 15 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
a very thin slice (of tissue or mineral or other substance) for examination under a microscope
“sections from the left ventricle showed diseased tissue”
a distinct region or subdivision of a territorial or political area or community or group of people
“no section of the nation is more ardent than the South”
a small team of policemen working as part of a police platoon
a land unit equal to 1 square mile
(geometry) the area created by a plane cutting through a solid
a small class of students who are part of a larger course but are taught separately
“a graduate student taught sections for the professor's lecture course”
a division of an orchestra containing all instruments of the same class
a small army unit usually having a special function
a specialized division of a large organization
“you'll find it in the hardware department”
a segment of a citrus fruit
“he ate a section of the orange”
the cutting of or into body tissues or organs (especially by a surgeon as part of an operation)
Synonyms, antonyms and the broader and narrower relations for section come from Princeton University’s WordNet. Full sources and licences.