a large dog of a breed typically used as guard dogs or for police work. The German Shepherd is a breed of medium to large-sized working dog that originated in Germany. Alsatians (people), a person from the Alsace region of France or a speaker of the Alsatian language. Alsatian definition: An Alsatian is a large, usually fierce dog that is often used to guard. Alsatian definition is - relating to, situated in, inhabiting, or coming from Alsace.