(archaic) A thing that is extremely holy; used almost exclusively in Holy of Holies.
Esimerkit
I'm planning to visit the holy city of Mecca this Ramadan.
Holy cow, I can’t believe he actually lost the race!
The holy of holies, a cubical space of ten cubits on the side, was separated from the larger antechamber by four columns, which were also covered with gold and stood upon silver sockets; they bore a second curtain of four colors.