Source : Webster's Revised Unabridged Dictionary (1913)

Twifallow \Twi"fal`low\, v. t. [imp. & p. p. {Twifallowed}; p.
   pr. & vb. n. {Twifallowing}.] [AS. twi- (see {Twice}) two +
   fallow.]
   To plow, or fallow, a second time (land that has been once
   fallowed).