Hister (genitive Histri) is the Latin name for the Danube (especially its lower course), or for the people living along its banks.
It also appears as Ister, equivalent to the Ancient Greek ᾽´Ιστρος, which also meant the Danube or the region around its mouth. The Ancient Greek colony of Histria in today's Romania was named using this form of the river's name.
The term may be related to the name of the region Istria in what is now northwestern Croatia, where a tribe called the Histri lived in ancient times. Some once thought that the local freshwater streams in Istria derived from a (non-existent) southward branch of the Danube.
In modern English the term is most commonly encountered in its use by Nostradamus, especially in a phrase at quatrain II.24 commonly translated "most of the battle (or armies) will be against Hister":Bestes farouches de faim fluves tranner:
Plus part du camp encontre Hister sera,
En caige de fer le grand fera treisner,
Quand Rin enfant Germain observera.
or, in English:
Beasts wild with hunger shall cross the rivers:
Most of the fighting shall be close by the Hister [Danube],
It shall result in the great one being dragged in an iron cage,
While the German shall be watching over the infant Rhine.
This is often interpreted to be a prediction of the war against Adolf Hitler's Nazi state in the twentieth century. However, none of the reputable sources listed support this view. In fact all of them point out that the name 'Hister' (as Nostradamus himself explains in his Almanac for 1554) in fact refers in his writings to the Danube, being mentioned (as elsewhere) alongside 'R[h]in' (Rhine) -- two rivers that formed the north-eastern frontier of the ancient Roman Empire. Un bien sçavant homme dans ce dernier quart se pourmenant le long de la riviere Hister dite Danube, he writes at Prose Presage 222, la terre se parfondant, dans ladite riviere se perdra ('A very scholarly man during this last quarter, while walking along the river Hister known as Danube, the ground subsiding, in the said river shall be lost'). This is evidently based on a historical incident described by Nostradamus himself in his Traité des fardemens (Proem, p. 19, 1552), involving one Gaspar Ursinus Vellius consellier à Vienne en Austriche, qui un soir soy pourmenant le long du Dannube la terre se fendit, & tumba & se nya ('a councillor at Vienna in Austria who one evening was walking along the Danube, the ground split apart and he fell in and was drowned').