The term "class" in the sociological sense originated in contrast to the old system of "estates". Originally, it referred to the "tax class" of a (male) person,

The term "class" in the sociological sense originated in contrast to the old system of "estates". Originally, it referred to the "tax class" of a (male) person, which formed the basis for census voting rights in both the USA and Europe until well into the 19th century. This is the reason why speaking of an "aristocratic class" remains somewhat inappropriate. The term "class" was introduced specifically to mark the difference between the old society, which was dominated by heritage ("estate"), and the new society, in which this has been replaced by wealth ("class"). That there was a lot of continuity from the old to the new order is another matter. Britian seems to be very special, because there the "upper class" is a mixture of old estate and new wealth (plus celebrities from academic, sport and culture), something that is more or less absent in the rest of Europe. While a poor Lord in England is still a Lord, a poor Graf in Germany is just a poor person.