WordNet records no synonym and no antonym for stratify. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
divide society into social classes or castes
“Income distribution often stratifies a society”
form layers or strata
“The rock stratifies”
develop different social levels, classes, or castes
Synonyms, antonyms and the broader and narrower relations for stratify come from Princeton University’s WordNet. Full sources and licences.
“Society stratifies when the income gap widens”
form, arrange, or deposit in layers
“The fish are stratified in barrels”
render fertile and preserve by placing between layers of earth or sand
“stratify seeds”