The term 'ambulance accessory' can refer to a variety of items that are used in conjunction with an ambulance. One such item is a SIREN, which is a five-letter word. A SIREN is a loud, high-pitched sound that is used to alert people to the presence of an emergency vehicle. It is typically mounted on the roof of the ambulance and can be heard from a great distance. The SIREN is used to warn other drivers to move out of the way so that the ambulance can reach its destination quickly and safely.