kai·ser / ˈkīzər/ • n. 1. hist. the German emperor, the emperor of Austria, or the head of the Holy Roman Empire: [as title] Kaiser Wilhelm. 2. see kaiser roll.DERIVATIVES: kai·ser·ship / -ˌship/ n.

kaiser the German Emperor, the Emperor of Austria, or the head of the Holy Roman Empire; in British usage, the Kaiser refers particularly to Wilhelm II of Germany (1859–1941), especially in the context of the First World War.

The word is originally recorded from Middle English (in form cayser), from Old Norse keisari, based on Latin Caesar; the modern English form (early 19th century) derives from German Kaiser.
Kaiser's War a name for the First World War.

Kaiser German title equivalent to Emperor. It derives from the Roman title ‘Caesar’ and was first connected with Germany when Otto I became Holy Roman Emperor in 962. The last Kaiser was Wilhelm II (r. 1888–1918), whose father had adopted the title after the Franco-Prussian War (1870–71).

kaiser emperor. XVI. — G. kaiser and Du. keizer, †ke(i)ser, a Gmc. adoption of L. Cæsar through Gr. kaîsar, repr. by OE. cāsere, OS. kēsur, OHG. keisar, ON. keisari, Goth. kaisar.