establishment has 11 distinct synonyms spread across 5 of its 7 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.
the act of forming or establishing something
“the constitution of a PTA group last year”
an organization founded and united for a specific purpose
the persons (or committees or departments etc.) who make up a body for the purpose of administering something
“he claims that the present administration is corrupt”
a public or private structure (business or governmental or educational) including buildings and equipment for business or residence
(ecology) the process by which a plant or animal becomes established in a new habitat
Synonyms, antonyms and the broader and narrower relations for establishment come from Princeton University’s WordNet. Full sources and licences.