From The Collaborative International Dictionary of English v.0.48:
Placet \Pla"cet\, n. [L. placet it pleases.]
1. A vote of assent, as of the governing body of a
university, of an ecclesiastical council, etc.
[1913 Webster]
2. The assent of the civil power to the promulgation of an
ecclesiastical ordinance. --Shipley.
[1913 Webster]
The king . . . annulled the royal placet. --J. P.
Peters.
[1913 Webster]