The Collaborative International Dictionary of English v.0.48:

Placate \Pla"cate\, v. t. [imp. & p. p. Placated; p. pr. & vb.
   n. Placating.] [L. placatus, p. p. of placare to placate,
   akin to placere to please. See Please.]
   To appease; to pacify; to concilate. "Therefore is he always
   propitiated and placated." --Cudworth.
   [1913 Webster]