thryfallow

from The Collaborative International Dictionary of English v.0.48

Thryfallow \Thry"fal`low\, v. t. [Perhaps fr. thrice + fallow.
   Cf. {Trifallow}.]
   To plow for the third time in summer; to trifallow. [R.]
   [Written also {thrifallow}.] --Tusser.
   [1913 Webster]