c. 1300 (n.) "the mercy seat," from Late Latin propitiatorium (translating Greek hilasterion in Bible); noun use of neuter singular of propitiatorius "atoning, reconciling," from propitiatus, past participle of propitiare (see propitiation). As an adjective in English from 1550s.[propitiatory etymology, propitiatory origin, 英语词源]