formation has 6 distinct synonyms spread across 3 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.
an arrangement of people or things acting as a unit
“a defensive formation”
the act of forming or establishing something
“the constitution of a PTA group last year”
natural process that causes something to form
“the formation of gas in the intestine”
creation by mental activity
“the formation of sentences”
Synonyms, antonyms and the broader and narrower relations for formation come from Princeton University’s WordNet. Full sources and licences.