Greek word
hilastḗrion
ἱλαστήριον
What it means
an expiatory, i.e. an atoning victim, or the lid of the Ark
an expiatory (place or thing), i.e. (concretely) an atoning victim, or (specially) the lid of the Ark (in the Temple)
Where it comes from
neuter of a derivative of hiláskomai (ἱλάσκομαι)