The Collaborative International Dictionary of English v.0.48:

Placate \Plac"ate\, n.
   Same as Placard, 4 & 5.
   [1913 Webster]

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]

WordNet (r) 3.0 (2006):

placate
    v 1: cause to be more favorably inclined; gain the good will of;
         "She managed to mollify the angry customer" [syn: pacify,
         lenify, conciliate, assuage, appease, mollify,
         placate, gentle, gruntle]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "placate":
   allay, appease, assuage, calm, comfort, conciliate, cool, defuse,
   dulcify, lay, lay the dust, mollify, pacify, pour balm on,
   propitiate, smooth, smooth down, smooth over, soothe, sweeten,
   tranquilize