WordNet records no synonym and no antonym for caste. 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.
social status or position conferred by a system based on class
“lose caste by doing work beneath one's station”
(Hinduism) a hereditary social class among Hindus; stratified according to ritual purity
Synonyms, antonyms and the broader and narrower relations for caste come from Princeton University’s WordNet. Full sources and licences.
a social class separated from others by distinctions of hereditary rank or profession or wealth
in some social insects (such as ants) a physically distinct individual or group of individuals specialized to perform certain functions in the colony