The Collaborative International Dictionary of English v.0.48:

Cessor \Ces"sor\, n. [From Cess, v. i. Cf. Cesser.] (Law)
   One who neglects, for two years, to perform the service by
   which he holds lands, so that he incurs the danger of the
   writ of cessavit. See Cessavit. --Cowell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cessor \Ces"sor\, n. [From Cess, v. t.]
   An assessor. [Obs.]
   [1913 Webster]