Ob·sid'i·o·nal adjective [ Latin obsidionalis , from obsidio a siege, obsidere to besiege: confer French obsidional . See Obsess .] Of or pertaining to a siege. Obsidional crown (Rom.Antiq.) , a crown bestowed upon a general who raised the sie... Found on http://www.encyclo.co.uk/webster/O/5