The Collaborative International Dictionary
Formedon
Formedon \For"me*don\, n. [OF., fr. Latin. So called because the plaintiff claimed ``by the form of the gift,: L. per formam doni.] (O. Eng. Law) A writ of right for a tenant in tail in case of a discontinuance of the estate tail. This writ has been abolished.
Wiktionary
formedon
n. (context legal historical UK English) A writ of right for a tenant in tail in case of a discontinuance of the estate tail.