holy of holies is a noun meaning "(figurative) something regarded as sacred or inviolable". It carries 2 recorded senses.
(figurative) something regarded as sacred or inviolable
“every politician fears to touch that holy of holies, the Social Security System”
(Judaism) sanctuary comprised of the innermost chamber of the Tabernacle in the temple of Solomon where the Ark of the Covenant was kept
Judaism
Definitions, synonyms and semantic relations for holy of holies come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.