Where does “ἄδυτον” come from?

ἄδυτον (Ancient Greek) comes from Ancient Greek ἄδυτος, from Ancient Greek ἀ-, from Proto-Hellenic hə-, from Proto-Indo-European sm̥-, from Proto-Indo-European sem- — together, one.

ἄδυτον (Ancient Greek): innermost sanctuary, shrine; inflection of ἄδυτος...