"superlatively sacred or inviolable," c.1600, from Latin sacrosanctus "protected by religious sanction, consecrated with religious ceremonies," from sacro, ablative of sacrum "religious sanction" (from neuter singular of sacer "sacred") + sanctus, past participle of sancire "make sacred" (for both, see sacred). Earlier in partially anglicized form sacro-seint (c.1500).