\Ob*sid"i*o*nal\, a. [L. obsidionalis, from obsidio a
siege, obsidere to besiege: cf.F. obsidional. See {Obsess}.]
Of or pertaining to a siege.

{Obsidional crown} (Rom.Antiq.), a crown bestowed upon a
   general who raised the siege of a beleaguered place, or
   upon one who held out against a siege.