Definition of Formedon in the reverter
A writ of formedon which lay where there was a gift in tail, and afterwards, by the death of the donee or his heirs without issue of his body, the reversion fell in upon the donor, his heirs or assigns. In such case, the reversioner had this writ to recover the lands. 3 Bl.Comm. 192.
That's the definition of Formedon in the reverter in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.