Definition of Formedon
An ancient writ in English law which was available for one who had a right to lands or tenements by virtue of a gift in tail. It was in the nature of a writ of right, and was the highest action that a tenant in tail could have; for he could not have an absolute writ of right, that being confined to such as claimed in fee-simple, and for that reason this writ of formedon was granted to him by statute and was emphatically called "his” writ of right. The writ was distinguished into three species, viz.: Formedon in the descender, in the remainder, and in the reverter. It was abolished in England by St. 3 & 4 Wm. IV, c. 27. 3 Bl.Comm. 191.
That's the definition of Formedon in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.