'placated' originates from Latin, specifically the word 'placare' (past participle 'placatus'), where the root 'plac-' meant 'to please' or 'to calm'.

'placate' entered English in the 17th century from Late Latin 'placatus' (past participle of 'placare'), passing into modern English usage as 'placate' and forming past/p.p. 'placated'.

Initially it meant 'to please or calm'; over time it evolved to the current sense 'to appease or pacify (often by concessions)', retaining the idea of reducing anger or hostility.