Strong's G2435 — ἱλαστήριον (noun)
hilasterion (hil-as-tay'-ree-on) n.
1. an expiatory (place or thing)
2. (concretely) an atoning victim
3. (specially) the lid of the Ark (in the Temple)
[neuter of a derivative of G2433]
KJV: mercyseat, propitiation 
Root(s): G2433 
Hebrew root: ἱλάσκομαι
Occurrences: 2