hostage: [13] Despite its similarity, hostage is not related to any of the English words host. It comes via Old French hostage from *obsidāticum, a Vulgar Latin derivative of late Latin obsidātus ‘condition of being held as a security for the fulfilment of an undertaking’. This is turn was based on Latin obses ‘hostage’, a compound noun formed from the prefix ob- ‘before’ and the base of sedēre ‘sit’ (English obsess [16] is made up of virtually the same elements). The use of hostage for the ‘person held’ was established before English took it over. => obsess
