sacrosanct (adj) – extremely sacred or holy; inviolable; beyond reproach or alteration
BREAKDOWN: SACR- (holy) + SANCT- (sacred or holy)
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This word is built on the root SANCT-, which means sacred or holy.
Common SANCT- words include include saint and sanctuary.
More esoteric SANCT- words include sanctificate, sanctity, and sanctiloquence.