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The Collaborative International Dictionary
Trifallow

Trifallow \Tri"fal`low\, v. t. [imp. & p. p. Trifallowed; p. pr. & vb. n. Trifallowing.] [Pref. tri- + fallow. Cf. Thryfallow.] To plow the third time before sowing, as land.
--Mortimer.

Wiktionary
trifallow

vb. (context obsolete rare English) To plough (land) the third time before sowing.