We don't have synonyms for castus yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are cactus, cistus and casts.
(N) :
an enslaved Gallic man who, together with the Thracian Spartacus, the fellow Gaul Crixus, and Celt Gannicus, alongside Oenomaus, was one of the leaders of rebellious slaves during the Third Servile War.
(N) :
an enslaved Gallic man who, together with the Thracian Spartacus, the fellow Gaul Crixus, and Celt Gannicus, alongside Oenomaus, was one of the leaders of rebellious slaves during the Third Servile War.