ἱλαστήριον hilastḗrion

Meaning

an expiatory (place or thing), i.e. (concretely) an atoning victim, or (specially) the lid of the Ark (in the Temple)

In the King James Version: mercyseat, propitiation

Derivation: neuter of a derivative of G2433 (ἱλάσκομαι);

Where it is used

• Romans 3:25 God presented Him as an atoning sacrifice in His blood through faith, in order to demonstrate His righteousness, because in His forbearance He had passed over the sins committed beforehand.
• Hebrews 9:5 Above the ark were the cherubim of glory, overshadowing the mercy seat. But we cannot discuss these things in detail now.