Placate

Make someone less angry or hostile.

First attested in the late 17th century; borrowed from Latin plācātus, perfect passive participle of plācō (“appease, placate”, literally “smooth, smoothen”) (see -ate (verb-forming suffix) and -ate (adjective-forming suffix) for more), ultimately thought to be from Proto-Indo-European *plāk- (“smooth, flat”), from *pele- (“broad, flat, plain”). Related to Latin placeō (“appease”), Old English flōh (“flat stone, chip”). More at please.

pacify, appease, assuage, soothe, conciliate